Add optional possibility to make adhoc property values permanent from the annotation dialog

[mpetris]

[danbalogh]

Desirable :) Edit: the tick box to do this should ideally remember its state, so that if I ticked it once, then it would come up as ticked by default the next time I create or edit a property. A possible alternative to making adhoc property values permanent would be to keep a list of all values used for a particular property and offer those as a dropdown list in the field for entering property values. That way, the user(s) can be sure to use a consistent terminology/spelling within a project even if the property values are not made into canon.