gui settings: fix show_panel to accept boolean

Follow the same behaviour as .Show() which show_panel() wraps.

Fixes the calibration file selectors on SPARC.
Small history overlay test case modifications for performance testing
Small change to the XRCed launch script that automatically adds the Delmic XRC plugins on launch
gui gallery: add support for spectrum background file

The spectrum need to be subtracted to a background before the efficiency correction can be really used.

This is only the GUI part. For now it will fail as the stream doesn't support background subtraction.
Handle NavCam HFW
Merge branch 'master' of delmic-server.local:odemis
Merge branch 'master' of vpn.delmic.com:odemis