XAS-57 test when creating the editor if the widget allows expressions.

Method was already in the interface, but was not used!

Now in NumberBox, if expressions are swicthed off for a given widget the
number will turn red if invalid.
parse value as number not string
Improved error message to user
Merge remote-tracking branch 'origin/1.2'

Conflicts:
	uk.ac.gda.common.rcp/src/uk/ac/gda/richbeans/components/scalebox/NumberBox.java