Unify OGRE initialisation
Currently the code for some part of the OGRE initialisation (namely plugin handling) is duplicated both in OpenMW and in the launcher. If we were to go down this route, we soon have 3 copies of the same code (OpenMW, launcher, OpenCS). That is obviously a maintenance nightmare. The code must be moved to a suitable component instead, so it can be used by all 3 applications without any code duplication.
(RM-873 from redmine: created on 2013-08-07 by Marc Zinnschlag, , closed on 2013-10-30 by scrawl .)