Switch from Poco->boost regex engine.

There is a bug in Poco::RegularExpression that causes and out of memory
error on some regular expressions. The boost version does not suffer
from this and actually has cleaner syntax for the eol conversion.
Refs #7019
Switch out usage of Poco regex for boost in GUI ScriptCode class

Not technically related to this ticket but the regexes were identical so
the ScriptCode class would have suffered the same out of memory error.
Refs #7019