New neutral default theme

- desaturated UI elements to grey
- desaturated all near-white icons to grey
- changed some hardcoded colors
New iteration of the theme

- try to implement ndee's mockup from the forum
- new color palette
- get rid of most gradients

probably needs some more tweaks
Fix visual glitch in Progressbar
Merge remote-tracking branch 'upstream/master' into new-default-theme
Merge remote-tracking branch 'upstream/master' into new-default-theme
More Theme fixes

- some color tweaks
- many margin fixes
- overall nicer look
Missing files and Tab changes
Merge remote-tracking branch 'upstream/master' into new-default-theme
More desaturated icons
Merge remote-tracking branch 'upstream/master' into new-default-theme
Fixed the progressbar to only require 16px in height
fix background alpha in dropdown arrows
Merge remote-tracking branch 'upstream/master' into new-default-theme
Merge remote-tracking branch 'upstream/master' into new-default-theme
Tweak Button margins & small fix for ToolButton
Merge remote-tracking branch 'upstream/master' into new-default-theme
Merge remote-tracking branch 'rollenrolm/new-default-theme'