MatplotlibPlot: IdleEvent removed

[Robin Hahn]

The IdleEvent is removed in Matplotlib 2.1. Since the signal eventIdle is connected to the idle_event function (backend_itom.py line: 234), some changes have to be applied.

At the moment python runs sometimes in an infinite loop when rescaling the matplotlibplot.

There is also an issue with the show function. This calls the mainloop function in backend_bases, which misses a 'self ' argument.

[M. Gronle]

First fixes included in itom repository: https://bitbucket.org/itom/itom/commits/6c6fb1a96bfd96dbad77957677f2fbc0a69212d5

[M. Gronle]

This problem does not exist any more in the matplotlib backend for matplotlib 3.x, which is currently supported by itom.