controllers: avoid setting request state in controller instances - set it in the thread global request variable

In TurboGears, controllers are singletons and we should avoid using instance
variables for any volatile data. Instead, use the "global thread local" request
context.

With everything in request, some use of c is dropped.

Note: kallithea/controllers/api/__init__.py still use instance variables that
will cause problems with TurboGears.