Add an a ui:pattern property to basic fields so form creator can give their own regexp

[timbl]

The form field code already has the ability to color user inout depending on whther it matches a regexp, and block filed submission for a bad user string. The patterns curently come from the form system internally for numbers, decimals, etc. This poposes addiing a property ui:pattern so the form designer can specify them.

This would be useful, for example, when prompting for things like Matrix or Blu Sky user IDs.

[timbl]

It seems ui:pattern is already in the ontology.