WEB: Added SEO functionality

[lwcorp]

Currently ScummVM doesn't use any SEO, meaning if you share pages they all externally preview as if you shared just the homepage, so therefore:

1. Switched to SEO title
2. Added SEO meta description
3. Switched to SEO og:title
4. Switched to SEO og:description
5. Switched to SEO og:url
6. Added SEO canonical URL

This should solve this ticket, but only the site owners can preview this, so please check first it works well for the homepage, articles, compatibility, etc.

I'm auto generating the description based on the same substr principle as in https://github.com/scummvm/scummvm-web/blob/master/templates/components/list_items.tpl

[lephilousophe]

Thank you for your PR.
Your proposal has several drawbacks while rendering the description: the tags are present and the content is not the most appropriate for several pages.
I proposed another approach in #411.

[lwcorp]

Thanks, but while your other approach adds certain features (which mine didn't) it simply ignores others. So why not just edit my PR to merge both of our features?

Otherwise your approach means:

1. You called your PR "Improve OpenGraph", but then added meta description too, so you should rename your PR accordingly.
2. Why not fixing <title> too (like I did)?
3. In meta description, you used if isset($description) so why not add else with my code of $content until the first linebreak?
4. Likewise for og:description
5. Likewise for og:title and if isset($subtitle) - why not add else with my code of $content_title?

[lephilousophe]

Thanks, but while your other approach adds certain features (which mine didn't) it simply ignores others. So why not just edit my PR to merge both of our features?

First, I am not fond of editing others' work behind their back.

Besides, your PR as it is doesn't work at all: there is a syntax error and cutting the line doesn't work for a reason I didn't investigate. I suspect you didn't try it in a development environment.

Finally, as I rewrote a big part of your PR, the only thing remaining is the fix for the URLs: that's not really an iteration over your work anymore. So pushing on your PR would be like a false pretense.

Otherwise your approach means:

1. You called your PR "Improve OpenGraph", but then added meta description too, so you should rename your PR accordingly.

IMHO what is OpenGraph and what is not is not really significant. All of these are web page headers to help other websites to render the page.

2. Why not fixing `<title>` too (like I did)?

When I first tested your PR, I noticed that content_title was not the most adequate as it added redundancy in the browser title (for example in the screenshots page, it says ScummVM :: Screenshots :: Screenshots, and that's not the only page).
I then decided to remove it as it doesn't bring much information to the user.
I changed the way the subtitle work afterwards and I didn't reconsider this change which didn't seem to bring much information. The page title is usually on the title bar and tabs where it is cut shortly. This means that having a long title isn't useful in this case.

After looking at it more, it may help rendering of search results in Bing (interestingly, Google seems to choose a better title than us).

3. In meta description, you used `if isset($description)` so why not add `else` with my code of `$content` until the first linebreak?

4. Likewise for og:description

Because your solution doesn't work where I didn't set a description.
First, it doesn't work like it is intended to as I explained above.
Then, it doesn't strip tags nor escapes them which means that it breaks the page layout when content contains HTML which is... always: content variable is the result of the rendering of another template.
Keeping the first line would only keep a tag.
Finally, on the pages where a description is missing in my PR, there is no valuable text either in the page to display, so your solution can't work either.

5. Likewise for `og:title` and `if isset($subtitle)` - why not add `else` with my code of `$content_title`?

Because content_title is a duplicate in the cases where a subtitle is not set.
Why do you want to add a subtitle on the screenshots global page? There is no need for one and it will only lead to redundancy in the title.

[lwcorp]

After looking at it more, it may help rendering of search results in Bing

Plus you did fix og:title so just apply even your own fix to <title> as well.