Enable/disable element in PeriodicTableWidget
Small fixes

Changed ExClickLabel to only emit clicked on left click released, and
either way call super with event.

In SignalWrapper, fixes to save/restore geometry was attempted.
ElementPickerWidget get EDX line selector

Implemented a context menu on elements to allow user to select which
xray lines to use for the elements.
Captialize element names in PeriodicTableWidget

Names are displayed in tooltip.
Bugfixes in xray line selection