#170, added test cases for StoreEventListener on expiration and eviction

Hi Please review this pull request, few things to notice:

1. I moved TimeSource from impl to core module as i needed access to TimeSource for writing expiration tests.
2. There is a bug in testPutIfAbsentOnEviction test, as putIfAbsent call puts key/value in store even thou store capacity is reached.

Thanks

Gaurav
 
What I meant is that those changes are added to tests that are unrelated to the issue, e.g. in this case the expiration is changed for a BulkComputeIfAbsent test. Testing the StoreEventListener should be decoupled from any other test.