Picker and curve z order.
Merge branch 'master' of https://github.com/t20100/pymca

Conflicts: PyMca5/PyMcaGraph/backends/MatplotlibBackend.py
Add "selectable" keyword.
Prepare color handling.
Make curve non-selectable when having many points.
Typo addCurve selectable
GL: addCurve selectable param + merged picking for images and curves
Matplotlib prefers colors as floats.
rename minMax.* to MinMax.*
Merge remote-tracking branch 'upstream/master'