* configureMimeType -> configureGenericHighlighter, since that is what
  it actually does.
* setupAsPlainEditor -> setupGenericHighlighter, since that is what it
  actually does
* avoid multiple highlighting definition lookups
* unify code paths by not separately creating generic highlighters
  through the factories

Change-Id: I9579ca5736bbf08c01b8e41b63c6b9f36bdc725e
Reviewed-by: Tobias Hunger <tobias.hunger@theqtcompany.com>