I18N: Move specification of engine specific files to enginedir/POTFILES.

This allows to keep the engines to specfiy the files for translation close to
the engine sources itself.

Thanks to criezy for his suggestion on this approach.
FULLPIPE: Move PreloadItems to gameloader.h
FULLPIPE: Implement CGameLoader::preloadScene()
FULLPIPE: Move Sc2 to gameloader.h
Merge pull request #378 from lordhoto/pluggable-engines-translations

RFC: Pluggable Engines: I18N: Move specification of engine specific files to enginedir/POTFILES
FULLPIPE: Fix leaked resource. CID 1063205
FULLPIPE: Move PreloadItem methods where they belong
FULLPIPE: Fix condition. CID 1063217
TSAGE: Initial implementation of R2R balloon cutscene code
NEVERHOOD: Move StaticScene into scene.h/.cpp
NEVERHOOD: Add console commands to handle resources
NEVERHOOD: Rename the "room" command to "scene" and enhance it

The naming has been changed from "room" to "scene", in order to keep it
consistent with the rest of the engine. The scene command now also
displays resource information about the current scene when invoked
without parameters
TSAGE: Initial bugfixes and renaming for R2R balloon scene
TSAGE: Bugfix for parameter type change in BackgroundSceneObject
TSAGE: Further renaming for R2R balloon scene
FULLPIPE: Added few destructors.
FULLPIPE: Initialize class variable. CID 1063187
FULLPIPE: Initialize 'selector'. CID 1063200
TSAGE: Further renaming and work on R2R Balloon Scene
FULLPIPE: Implement FullpipeEngine::defHandleKeyDown()