Temporarily disable Blender BMesh conversion

Disable BMesh conversion while associated unresolved issues receive due
attention. Referencing #400, #373, #318  #315 and #132.
Merge pull request #402 from jdduke/disable_bmesh

Temporarily disable Blender BMesh conversion
CMakeList: Support setting Libs.private
assimp.pc.in: Add static libs to Libs.private
Merge pull request #405 from TimothyGu/patch-1

Correctly set Libs.private field in pkgconfig file
update: add some files to .gitignore.

Signed-off-by: Kim Kulling <kim.kulling@googlemail.com>
bugfix: fix compiler warning: converting double to float.

Signed-off-by: Kim Kulling <kim.kulling@googlemail.com>
bugfix:
- remove and comment some gcc compiler warnings for not used vaiables.