Issue #147 - Add non-bulk Ehcache unit tests

Adds unit tests for the following Ehcache methods:

* get
* put
* containsKey
* remove(key)
* clear
* iterator
* putIfAbsent
* remove(key, value)
* replace(key, value)
* replace(key, oldValue, newValue)
Naming fun: consider using `FakeStore` or `StubStore` instead of `MockStore` - I need to adjust mentally each time I read mock because it is not a mock in fact.