Adding feature for adding own CSS to brackets GUI (#10548)

[FabianCernota]

You can now adding own CSS declaration without using a extension.

Put an custom.css on the same level like config.json or index.html and activate it over View -> Themes

Reload the UI with F5

[peterflynn]

I'm not sure we need a checkbox in the UI -- why not just load the file any time it exists? The keymap.json file works that way and it seems fine.

To match how preferences and keybinding overrides work though, I wonder if we should listen for user changes to this file and update the Brackets UI immediately, without requiring a reload. It's not hard -- e.g. here's how KeyBindingManager does it -- and re-replacing the original style tag should be easy too. The only question is whether messing with CSS is so error-prone that it shouldn't go into effect without an explicit reload gesture...

[FabianCernota]

Okey i will change it so that the CSS File will load if exists.

[redmunds]

@FabianCernota Not sure if you saw my comment in IRC, but I think ExtensionUtils methods addLinkedStyleSheet() and addEmbeddedStyleSheet() will need to be fixed to detect "custom.css" and insert any new stylesheets before that stylesheet. Otherwise, "custom.css" will not override all extensions and themes.

[sprintr]

I think it will be nice to put custom.css in extensions directory, (where we already have disabled and user directories) so it can be accessible from Brackets UI.