Future use cases will require the ability to find compatible module builds
to buildrequire based on the base module the module used to build. This
commit adds an association table that will contain module build IDs
and the base module they buildrequire.
Addresses FACTORY-3353
1. Changed ModuleBuild's context property to db column, it's
non-nullable and default value is '00000000' to keep it consistent
with previous behaviour.
2. Changed ModuleBuild.contexts_from_mmd to return a tuple of
(ref_build_context, build_context, runtime_context, context).
3. Updated tests affected by this change.
- DB migration scripts.
- Models: ComponentBuildTrace, ModuleBuildTrace.
- ModuleBuild.state_trace method for querying for a particular module's
state history.
- SQLAlchemy before commit session event handler for recording
module/component state changes.
- REST API verbose mode for getting state trace of a particular module.
- Tests use make_session, so that event handlers are in effect.
- Short info in README about verbose mode.
- Tests verifying whether state trace information about a module appears
in verbose mode.
- Other minor fixes (RidaBase -> MBSBase, PEP8...)
