Add optional regexp validation to service dialogs

Text boxes now expose a drop-down for validator type and
a text field for validator rule. When 'Regular Expression'
is selected for the validator type, user input will be
matched against the provided validator rule. This is similar
to how Foreman validates user input for Smart Variables.

https://bugzilla.redhat.com/show_bug.cgi?id=1085158
@dillaman @Fryguy This format does not allow us to specify options on the regex.  Is there a way to pass the entire regex so the string can contain options or would that require another field on the dialog?  I have not been able to find a single-string solution so far.