get_reasonable_array_context_class improvements (#230)

* get_reasonable_array_context_class improvements
- add documentation
- add logging
- check for correct loopy branch

* reword doc

Co-authored-by: Andreas Klöckner <inform@tiker.net>

* clarify which branches are needed

* add warning about missing branches

* check for mismatched loopy/meshmode branches

Co-authored-by: Andreas Klöckner <inform@tiker.net>