Added mocking for test to isolate redis and db

Also added example to illustrate using in memory sql db
initialised in test setup. So memory store in storage module not needed.

Commented out get_last from server and test. Needs revisting as last is no longer
at head of a single list of titles.

Moved mock to requirements_test.txt

requirements
Merge pull request #5 from LandRegistry/unit-test-and-other-cleanup

Added mocking for test to isolate redis and db