make SingletonConfigurable a subclass of LoggingConfigurable

[Carreau]

Most subclass of SingletonConfigurable are Applications that redefine a log trait.

Exception is InteractiveShell in IPython which define the old way a self.logger. And LaTeXTool in IPython that does not use log.

Once this is done we can do that in load config (roughly):

if name in traits:
   ...
elif isinstance(self, LoggingConfigurable):
       from difflib import get_close_matches
       m = get_close_matches(name, traits)
       if m:
           self.log("{} not in config, do you mean one of: {}".format(name, m))  

[minrk]

fine with me.