Adds stub for Sql Server 2014 support

This adds a new SqlServer2014ProcessorFactory which means that the
provider/db argument to the runner now accepts the string
SqlServer2014.

A new SqlServer2014Generator class is added too but all it does is
inherit from the SqlServer2012Generator without adding any new
functionality.
integration tests run on Sql Server 2014 too

Adds SqlServer2014 to the IntegrationTestBase class so that all
the integration tests can be run against Sql Server 2014.
Merge pull request #561 of daniellee/sqlserver2014

* https://github.com/schambers/fluentmigrator:
  integration tests run on Sql Server 2014 too
  Adds stub for Sql Server 2014 support