Added Session.ExecuteAsync using TPL

- Added 3 integration tests
- Added visual studio tmp files to .gitignore
Merge branch '2.0' into 2.0-reorg

Conflicts:
	Cassandra.MSTest/Cassandra.MSTest.csproj
	src/Cassandra/Properties/AssemblyInfo.cs
	src/Cassandra/Session.cs
Added the test to the new folder