Remove dedicated applet target, add debug HTML file

All JAR targets will now sign the JAR file. Also, update the useless key.
Clean up the PDF manuals with the clean target
Honor debug compile-time setting
De-concretize configuration parameters handling

Add an interface (well, abstract class) for mechanisms that handle the
configuration parameters. This will allow to transparently implement an
in-memory store, that will be used when the java.prefs API is not available
or not desirable (e.g., in the applet or in unit tests).
In-memory ConfigStore implementation
Return in-memory ConfigStore if Prefs API is not available

Also: fix comments, add a method to get a temporary config store.
Use temporary config store in tests
Fix test HTML page and renew the useless key

Also, change the cname to EduMIPS64Team.