Themes scrollbars

[MiguelCastillo]

This is basically a redo of #8493, because I messed the history after rebasing instead of merging.

[MiguelCastillo]

cc @dangoor

[TomMalbran]

@MiguelCastillo @dangoor To fix the custom scrollbars issue I am thinking that we need to scope the default scrollbars to everything except for the editor using a :not() selector. By doing that we get by default the system scrollbars in the editor. And finally, we can add the custom scrollbars to the Light Theme less file.

[dangoor]

@TomMalbran Some of us were just discussing this. Rather than having the toggle being for "Use system scrollbars", we'll change the toggle to say "Use theme scrollbars". So, the switch is going to be between Brackets' default (customized) scrollbars which will come in both light and dark and the scrollbars that are provided by the theme.

[TomMalbran]

@dangoor That is a good option

[MiguelCastillo]

So, we want to go with "Use theme scrollbars"? That's the text I used in my first encarnation of the setting. It eventually mutated to what it is now. :)

I like it too.

cc @ryanstewart

[dangoor]

Change looks good. Merging