Adds a small field to change the number of sites to display

[giliam]

Simply adds an input field (number type) under the list of websites so you can display more or less websites. I've always found it limited to only display 5 sites.

[supertanuki]

Hi @giliam and thanks for this contribution.
But I am not sure that adding this feature is useful for everyone.
Before adding a feature, please see https://github.com/supertanuki/Carbonalyser#support--source-code
or let me know by adding an issue.
I let this PR opened. Any other opinions about this?

[giliam]

Thank you for your answer! It seemed pretty small to me and quite useful to know which websites are consuming too much energy to change my behaviours. Having only 4 sites displayed is kind of limited compared to the total number of sites we visit every day. But I understand :)

[ImaCrea]

Would be a great addition imho.