Add appdata file. Closes #1368
Merge pull request #1372 from pejakm/appdata3

Add appdata file. Closes #1368
[Windows] Fixed some issue with the blur background effect,

- Also moved all of codes related to blur effect of tabbar to ComboTabBar.
[RTL] Force AdBlockTreeWidget and treeTags to be as LTR widgets.
Added hack to fix QT_STYLE_OVERRIDE with QProxyStyle

Forcing a widget style with QT_STYLE_OVERRIDE env variable does
not work when the app is using a QProxyStyle.
Manually appending the -style=$QT_STYLE_OVERRIDE to command line
arguments workarounds the issue.

Closes #1357