MouseClickEvent: sometimes __repr__ could cause an exception

This happens during debugging session in an IDE (eric5) when debugger inspects
variables but self._scenePos is not yet initialized.
Make signature of the setPen method consistent
Make setPen() methods more consistent throughout the package.
Merge remote-tracking branch 'termim/develop' into develop

Conflicts:
	pyqtgraph/graphicsItems/ROI.py