Cleaned up unit/integration tests.

Added a credentials class with associated XML file to store Google
credentials locally that will be read in by the integration tests. The
_Credentials\GooCalCreds.xml file will be excluded by the GitHub ignores
file; you'll need to update the _Credentials\GooCalCreds.xml file in
your local project with your Google calendar/credentials. Did you really
think we'd give you our credentials?