Use priority ordering when retrieving SCM fields from POM files

[benmss]

The Java Repo Finder extracts SCM metadata from POM files in order to determine the related repository URL. By default, up to three URLs can be extracted from SCM section, but the list can be extended arbitrarily by Macaron users. In one particular case, it was discovered that one of the three default URLs was different from the other two, and also incorrect. Generally, it seems that the URL field is the most reliable choice, and allowing it to be checked first would Repo Finder accuracy in some cases.