Improve Atlas toolbar

[historic_bruno]

The Atlas toolbar could be improved in several ways:

• Move the simulation buttons from the map panel to the toolbar and give them "media player" style icons (e.g. play, pause, stop, fast forward).
• We'll want different sections for different types of buttons. This will require modifications of our custom toolbar which treats every button as a tool (e.g. paint, modify elevation, transform object). Do we need all the tool buttons?
• Investigate ​wxAUIToolbar, it's more complex so more likely to have bugs, but does supposedly offer advanced features. Documentation appears sparse and we need to check compatibility on various platforms and versions of wxWidgets.

[historic_bruno]

Here's an old mockup, containing a few clues for the proposed toolbar: ​http://i.imgur.com/j9CKh.jpg