Fixes an issue with horizontal scrollbar when it was hard to drag it by
mouse in Acri theme, because active area was thinner than the visible
scroll handle.
Adds the ability to set the current palette for the program via adding
"OBSTheme" objects to the qss files. The values for the OBSTheme object
are the values used by QPalette::ColorRole.
Modifying the global palette allows the ability to easily/quickly look
up application theme colors (especially if you would like to use them
for QML), as well as the ability to fix the hyperlink color issue. (On
dark themes, links would still be dark blue, causing them to be
difficult to see)
Fixing a reference to Rachni theme folder, some minor tweaks and
reverting volume meter foreground colors to original brightness.
Closesjp9000/obs-studio#1169
