clean up AggressiveDefaultDict
simplify data provider
Merge pull request #4132 from dimagi/opm-es

Update MockDataProvider with availability changes
Check for specific service availability
make the service availability dependence in tests more explicit
remove unused assignment
make service availability checks actually test the service key
Merge pull request #4133 from dimagi/opm-es2

Check for specific service availability
clarify comment and remove debug info
Merge pull request #4147 from dimagi/opm-cz

clarify comment and remove debug info
add tests for snapshotting
test and tweak snapshot functionality