Bugfix: use face-points accessor.

This only worked because of a bug in mesh scaling that replaced faces by
lists of their points.
Added caching for URDF models.
Got rid of string-based type unification again.

Since all object types need to be declared as designator properties
anyway, they will be eq.
Don't ignore poses of visual elements in URDF file.
modified `object-in-hand'

The designator was modified and contains now all the grippers. The `object-in-hand' return all the grippers in the designator.
modified the `update-grasped-object-designator' to store the grippers in the current designator
Merge branch 'master' of https://github.com/fairlight1337/cram_gazebo
Merged from Lorenz's repo
Merge branch 'master' of https://github.com/yazdani/cram_gazebo

Conflicts:
	simple_belief/src/utils.lisp
Removed the missing min-handles property handling

Items that are read from the simple-knowledge knowledge base now include the min-handles property again.
Removed obsolete newline
Made the use of the `simple-knowledge' module optional
Added bullet-reasoning as dependency
Added registration in bullet-reasoning for perceived objects