Redirects ServiceStack.Common.Extensions to ServiceStack.Common

On Issue #187

I noticed that all classes in the [ServiceStack.Common.Extensions](https://github.com/ServiceStack/ServiceStack/tree/master/src/ServiceStack.Common/Extensions) folder/namespace are now marked as obsolete.  A find and replace of [ServiceStack.Common.Extensions](https://github.com/ServiceStack/ServiceStack/tree/master/src/ServiceStack.Common/Extensions) with [ServiceStack.Common](https://github.com/ServiceStack/ServiceStack/tree/master/src/ServiceStack.Common) for all using statements in the [ServiceStack.OrmLite](https://github.com/ServiceStack/ServiceStack.OrmLite/tree/master/src/ServiceStack.OrmLite) solved the issue (#187).

I did find and replace for [ServiceStack.Common.Extensions](https://github.com/ServiceStack/ServiceStack/tree/master/src/ServiceStack.Common/Extensions) to [ServiceStack.Common](https://github.com/ServiceStack/ServiceStack/tree/master/src/ServiceStack.Common) for all using statements in the entire solution, too.

All test passed. The reported TypeLoadException is no more (an additional passed test; though not written)