Delete many (very) stale bits of documentation
Move the interesting bits of the branding graphics around, delete the
remaining.  The “Overture Components.ppt” file has been moved into PGL’s
jointpub repository.
Delete the quickSheetMaven, as it’s now on the wiki at
https://github.com/overturetool/overture/wiki/Maven-Survival-Guide
(see issue #251, and the previous two commits relate to that as well)
Normalise release note filenames