remove references to middleware that were missed previously
use key apis rather than local implementation of key conversion. remove local implementationa
remove spurious test for attribute
fix test setUp to avoid unneeded flattening
code quality fixes
add security check ensuring that the coach is coach for *this* CCX.
prevent ccx/deprecated course id problems
1. do not allow ccx objects to be created if the course id is deprecated
2. filter out any ccx memberships that involve deprecated course ids (in case there are bad ccxs in the database)
Fix test failures and errors arising from incorrect code path execution
Create context manager to handle unwrapping and restoring ccx values for the modulestore wrapper, employ it throughout modulestore wrapper implementation
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