NUCCORE-1210 Configuration.getManagerOverrideableProperties() uses quite a lot of cpu during ExecutionContext creation. Cache the calculation and reset it when underlying structures change.
Merge pull request #4 from kaarelk/NUCCORE-1210

[NUCCORE-1210] Configuration.getManagerOverrideableProperties() cache
[NUCCORE-1207] Update add/addAll to catch and rethrow exception in
backin store add as IllegalArgumentException (rather than just logging
it)
[NUCCORE-1209] Add further constructor caching for remaining method and
don't use ClassUtils from IdentityManagerImpl so we cache id
constructors in own (synchronised) cache