[Integration Tests, FieldHelper] Added SiteTestScope test helper to setup/teardown site collections for every integration test.
- Creating/destroying blank sites doesn't take too long (3-4 seconds), so it shouldn't be too costly
- Temp test site collections are created on default port 80 web app
- A few initial integration tests for FieldHelper in FieldHelperTest
- Reworked IFieldHelper to return the SPField from Ensure calls
Merge branch 'develop' of https://github.com/GSoft-SharePoint/Dynamite into develop