Pythat

Fixes of RadioButton behavior when loading

Add Explorer
- Multi window matplotlib application that shows colorplots of all axis combinations of an nd dataset
- lin/log switches for color scale
- capture, save and load views
- switch between views for A/B comparison
- use ctrl+arrow keys to move RectangleSelectors

- Add mask_all_zeros function to helpers.BLS

Bugfix in helpers.ROI

Added subtract_background function to helpers.BLS

handle "tree_view" object in measurement_tree

This is a bug fix release:
- Fixes Bugs due to wrong handling of multi segments ROIs
- Resolve a bug where a byte object in a metadata dictionary could not be dumped to json
- Replace special characters in metadata dictionary names