Fixed bug in _find_intersection.

This function is used to get the point there an arc encounters an edge of a transition.
Fixed bug of name validation.

Moved the non-empty string validation to the end of the function to be validated.
(After prefixes have been removed).
Added predicate_updater dialog and function.

There's now a functionality to set the initial marking of all predicate places (in all PNs), which is called before creating the full PN.