Add a mutex package with some global pins

[Tobias-Fischer]

Can we get rid of version specifiers in the robostack.yaml using the mutex package? Then we can have a combined robostack.yaml for noetic and galactic.

Currently the robostack.yaml's differ for:

• ogre (no specifier on galactic, 1.10 in noetic)
• pcl (no specifier on galactic, 1.11 in noetic)
• pyqt (5 on galactic, 5.12 in noetic)

Having a single robostack.yaml seems important, as we use a single rosdep on conda and that cannot distinguish robostack-noetic from robostack-galactic easily as far as I can tell.

[wolfv]

yeah that makes a lot of sense. We should have pins in the conda_build_config and in the mutex package only.

[Tobias-Fischer]

See #48

[Tobias-Fischer]

Rebuild is nearly complete, let's close this.