Fixup the windowmanager extension code

ie. don't have it in its own dir

+ fixup some errors in the string matching from when extensions where
renamed from a wl_ prefix to a qt_ prefix

Change-Id: I5707c24fa727b9e49bd267eeb23fc8e43c40354f
Merge pull request #1 from mikkoharju/master

Fixup the windowmanager extension code