Java2Swift improvements for producing configuration files from Jar files

[DougGregor]

Improve the experience of producing Java2Swift.config files from Jar files and better cope with layers of Swift-wrapped Java libraries. This includes:

• Filtering out nested classes from Jar files, since we cannot handle them yet
• Combining the class paths from all of the dependent Java2Swift.config files with the one being used and providing those to the JVM instance
• Fixing an issue where Java2Swift would generate func init() for a Java method named init