Clean up for get_simphony_panel

[kitchoi]

• get_mayavi2_engine_manager is renamed to get_simphony_panel:
  • the former is not self-descriptive for the end users (engine_manager may also be confused with the mayavi.tools.engine_manager in mayavi, all in all, bad name)
  • since get_mayavi2_engine_manager was only recently merged to master, was not included in the api and was not there in the previous release, I believe no one is using it and so no deprecation warning is necessary
• Expose get_simphony_panel to the plugin namespace (i.e. accessible from simphony.visualisation.mayavi_tools)
  • useful backup for getting the simphony panel in the Mayavi2 in case binding simphony_panel to the embedded python interpreter fails for whatever reason

[stefanoborini]

good for me, but I am not sure if I can start merging. @itziakos , @dpinte ?

[dpinte]

@stefanoborini sure, go ahead!