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)
I've moved the adjustment of lastAccessTime to FakeStore in get, putIfAbsent, computeIfAbsent, and the Iterator.next method returned from iterator().