Separate panel handling

[chrherold]

1. allow to use independent (polygon)-filters for each panel
2. allow independent statistics for each panel (choosable percentiles, mean, nr of points)
3. allow export of filtered data points in (two) column table for use in other plotting tools

[paulmueller]

1. This is possibly a duplicate of point 1 in issue Add Analysis tab #7? Please comment there.
2. This is a duplicate of issue Add Statistics tab #6.
3. I believe this also belongs to issue Add Statistics tab #6. Please comment there how the exported data should look like.

[paulmueller]

Moving the export request of point 3 to issue #22. I believe the others are duplicate.