[Themes] Removed waiting until to app is ready to apply themes in order to get ri...

...d of the flicker when the editor loads each time it is opened

https://github.com/adobe/brackets/issues/8377
FYI, I added some notes in there. https://github.com/MiguelCastillo/brackets/commit/64ffcf7e6a8bb968e1424035cba56379ebc20625#diff-82c3690745f7c8a1b46c19bba1804f0aR72