Double Click to Minimise/Zoom & Fixes for Missing Traffic Light and Dark Menu Bar

[andersio]

This PR:

1. Reintroduced the ability to Double Click In Titlebar to Zoom/Minimize*. (Application does not gets minimized. #54)
2. Fixed an issue preventing the traffic light from showing up in a circumstance. (Window buttons are gone after fullscreen #66)
3. Fixed the barely visible status item when using a dark menu bar. (Chit Chat Top Bar Icon Barely Visible in Dark Mode #80)
4. Fixed a few lines with inconsistent code style that came with my previous commits. Sorry about that. :(

* courtesy: https://bugzilla.mozilla.org/show_bug.cgi?id=853105, though as a side note the plist key has been changed for 10.10 and later.

[andersio]

Merged #84.

[stonesam92]

Thanks once again, @andersio!

I had to change windowWillEnterFullScreen: to windowDidEnterFullScreen: in order to get the traffic light buttons to show in fullscreen mode on 10.10, but other than that everything appears to work correctly.