Switch IAppMgrUI inheritance from Interface to INamedInterface and remove the pure virtual name()

IAppMgrUI inherits from IInterface, and adds a pure virtual name() method with the exact same signature as the one in INamedInterface.

As a result, the same effect can be obtained by inheritance from INamedIterface instead of IInterface. The advantage is that if an implementation (virtually) inherits not only from IAppMgrUI but also another interface which (virtually) inherits from INamedInterface, there is no ambiguity in the definition of name(). With the 'old' code, one has to disambiguate between multiple name() members...