QDoc: Remove QDocGlobals

This change moves the setting of configuration options from QDocGlobals
to Config. This allows for the removal of the entire QDocGlobals class.
Some methods (getters/setters) are part of the move, others were used
exclusively by Config:: and are therefore dropped entirely.

Also, move the ownership of QDocCommandLineParser from main() to
Config - this makes Config the authoritative source of all settings,
whether from the command line or .qdocconf variables, and makes it
possible to reset() the full state of the Config.

Finally, remove the QDocGlobals auto-test, as it is no longer needed.

Change-Id: I8e39931c828c763cb0462cbbdf3fe1a39b2ad70b
Reviewed-by: Topi Reiniö <topi.reinio@qt.io>
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>