customscript: Support for more mime types

The custom script formatter should actually accept any mime type, this
is currently not implemented in SourceFormatterController, though.

Sven, wanna have a look?

BUG: 335548
Move compiler related settings to it's own tab.

TODO: Port TableView to TreeView
Port compiler-selection dialog to QTreeView

REVIEW: 119449
Merge remote-tracking branch 'origin/4.7'