[Dev] CPIA widgets can now implement OnInit in addition to __init__

[John Anderson]

I ran into the usual problem, where my widget that corresponds to a 
block isn't completely wired up when its __init__ is called, e.g. the 
widget variable isn't set. So If you need to postpone some 
initialization until after your widget is completely build and wired up 
to the block, just implement an OnInit method and do your initialization 
there. I already moved over all the calls to mixinAClass from 
wxSynchronizeWidget.

John