References clean up

Removed unused references from
- Cassandra.DSE.csproj
- Cassandra.IntegrationTests.csproj
- Cassandra.Tests.csproj

Projects compile, unit tests pass
Tests clean up

- Added license header to the test files that were missing it
- Removed unused namespaces
- Moved ThreadPerTaskScheduler from Cassandra to Cassandra.Tests
Input validation

Checking parameter for null
Unit test coverage

- AbstractResponse (4 tests added)
- ResponseFrame ( 2 tests added)
added params check
fixing merge conflicts
Merge branch 'pull40_2'