Adds latest pneumatic gripper STLs and DAEs.
Adds electric gripper with fingers.
Adds 'old' pneumatic gripper meshes to provide continuity.
Renames pneumatic_gripper to pneumatic_gripper_base, matching electric gripper form.
Merge pull request #35 from RethinkRobotics/mesh_update

Adds latest pneumatic/electric gripper STLs and DAEs