Clean up

 - Add @Overrides where needed.
 - Update javadoc comments
 - Remove extra semi-colons
 - Rename DataConnection.java to DataConnectionBase.java
 - Rename GsmDataConnection.java to DataConnection.java
 - Add defaults to switch statements
 - Remove/fix most "if (false)" statements. Fixed by using a CONSTANT
 - Fix hidden variables by hoisting to base class or renaming
 - Tweak some debug output

Change-Id: If38de2fdeaacafbf40cdfd7f84dc5c52030ba2a3