Merge everything to kamaki.clients

Remove multiple hierarchies of connection classes (== abandon support for
    alternative connection methods, e.g. for requests from pypi)

New connection classes are
- RequestManager
- ResponseManager
Semantics:
    RequestManager constructor commits a request without performing it
      but it performs all sanity checks for url, path, method and params
    RequestManager.perform will perform the commited request, if called
    ResponseManager constructor needs a RequestManager instance
    ResponseManager.(various properties)
        request is pooled from a ContextManagerPool (objpool) when needed.
        Results are cached and used as long as the ResponseManager instance
        is alive

Remove KamakiConnection/ResponseErrors, use ClientError wrapers for everything

Remove the connection livetest

TODO: Adjust unittests