Adjust mosparo to handle a high number of projects (200+)

[zepich]

In #224, we discussed the limitation of mosparo in terms of the number of projects.

I estimate that mosparo has a problem with the number of projects, probably if you have more than 200 projects. In the question discussed, we're talking about 60,000 projects, which is impossible right now.

The idea is to optimize mosparo so that it's possible to manage more than 200 projects (even 60'000 projects).

For this, we have to do at least the following things:

• Locate the bottlenecks
• Change the project switcher dropdown in the top left corner. Replace the in-browser search with an XHR request to a backend controller to search the projects
• Adjust the project list page (boxes) and add a pagination
• Adjust storing the CSS files (/resources/{UUID}/{hash}.css) and the CSS mapping in public/index.php (use multiple files or try different approach)
• Test if everything works smoothly with a high number of projects, especially with the number of project memberships of a user