The graph adadptors can be alteration observed.
In most cases it uses the adapted graph alteration notifiers.
Only special case is now the UndirGraphAdaptor, where
we have to proxy the signals from the graph.

The SubBidirGraphAdaptor is removed, because it doest not
gives more feature than the EdgeSubGraphAdaptor<UndirGraphAdaptor<Graph>>.

The ResGraphAdaptor is based on this composition.

Some classes assumed that the GraphMaps should be inherited
from an ObserverBase. These classes parents replaced with
DefaultMap which cause that the graph maps should not be
inherited from the ObserverBase.

Traits for alteration notifiers
SplitGraph is temporarly deleted