Added Constants.java
Added Copyright notice
make sure that 404's aren't lost between threads from map DL's
Merge pull request #790 from lexware/patch-1

Added Constants.java
FIXED: offline mode

 * Do not toss error screen if displaying offline mode
 * Fix broken offline mode. (Offline mode dialog not displayed but
   game is starting)
   * Do correct signaling from  LoginWorker
FIXED: convert "\n" in XMLs to new lines

 * Description and warning tags can now include "\n"
ADDED: do not save mojangdata button

 * Added saveMojangData variable into User
 * Option controlled by ProfileAdder and ProfileEditor
 * If saving of mojangData is disabled, custom object writer will cleanup
   User object's mojangData before serialization