Updated to-do list based on recent post.

Leo build: 20140903084115
Simplified and reorganized  HighLevelInterface class:
Removed unused and irrelevant mutable_methods list.
Replaced toGuiIndex by toPythonIndex, including in unit test.
Removed HLI.set_focus synonym.  It was never used and it conflicts with c.set_focus and g.app.gui.set_focus.
All tests pass.

Leo build: 20140903090558