Removed datetime from InvalidStringIds collection

The string "2010-01-07 11:00:00 a.m." no longer appears to be an invalid
id according to the rules in MobileServiceSerializer.GetId.

Removing this value from the test data fixes nine failing tests.
Re-added datetime as an invalid id

ToString() was returning an invalid id according to developer's locale
settings at the time of writing. This fix adds the originally intended
value.
Merge pull request #347 from deadalusai/issue-datetime-as-invalid-id

Remove date/time string from InvalidStringIds collection