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 Yes, that's what I was talking about.  I'm good with keeping it the way it is now.  We can implement the options as a separate field later if it becomes necessary.  What I would like to see is "/" characters around the "Validator Rule" text box so it is clear to users that they do not need to include them in the text.  Similar to how http://www.rubular.com/ displays it.