Refactored StoreTests to test both persistence types
Added basic tests for EF

These are primarily copied from the classic .NET unit tests but
converted to run under MSTest rather than NUnit.
Added a stress test that replicates issue #120
Fix for issue #120

EnsureOutputStream should only attempt to open the output stream if it
is not already set in the class.
Test fixes

Allow more time for store worker to shutdown and delete files.
Fix for async copy of test data files.
Merge branch 'feature/issue120' into develop