Added DsDbItem and DsDbTemplate for using deserialized data in tests
Changed the way the serialized item files are resolved and removed the need to specify the database name when creating DsDbItem/DsDbTemplate
Unit tests added for Sitecore.FakeDb.Serialization
Merge pull request #20 from hermanussen/master

Added DsDbItem and DsDbTemplate for using deserialized data in tests