Sqlite syntax provider

This pull requests adds a sql syntax provider for Sqlite, which is intended for use with the Test project.
Umbraco.Core doesn't have any dependencies on Sqlite, and the nuget package with the Sqlite data provider has only been added to the Umbraco.Tests project.

Right now the possible use of this provider is very limited because the legacy datalayer is still heavily used throughout the codebase. The overall features of SQLite is also very limited and it won't be possible to use it as a file based db because upgrades won't work.

The ContentRepositoryTest has been re-implemented to use SQLite but not all tests in this test fixture currently passes, which is a bit weird. But I expect that it is related to the offset of Id's for the content and content types used in the tests (and possibly the ordering of the items in the various tables).
So while the provider works its not 100% solid.