Moved prefix regexes from Call.cs to CallsBureaus.xml and added
IsPrefix method to CallsBureaus class to test for prefix.
Moved check for prefix and call to CallsBureaus.xml and
CallsBureaus.cs. Modified Call and Pfx classes to call the
methods in CallsBureaus class to check for prefixes and calls that
may also be prefixes (VP2E is the only one at this time).
This completes changes for issue #125.