api: refactor the SWHRemoteClient so it does not inherit from ObjStorage nor SWHRemoteAPI

implement the remote api accessor as a _proxy attribute instead of inheriting
the class to make class instanciation easier and prevent name collision.

Also get rid of the ObjeStorage inheritance which did not help and add
instanciation (argument passing) complexity. This also solve the
'allow_delete' attribute presence which makes no sense for the remote api
component.