Force elementary stylesheet on all platforms

[AbrarSL]

Using elementary applications on other platforms with stylesheets other than https://github.com/elementary/stylesheet causes visual glitches and oddities. Issues such as #103 and #53 can also be fixed by changing this.

^This is on GNOME (Adwaita)

I've created #123 which is lifted from https://github.com/avojak/warble/pull/18

This would only be required until elementary figures out a universal solution for their platform, https://github.com/elementary/granite/pull/501