Ignore DAT files

* Getting these from http://aes.online-domain-tools.com/ with AES
  encrypted/decrypted data
Add AES-256 library

* Added ARM (Due)-compatible AES library
  (https://github.com/qistoph/ArduinoAES256)
* Added decryption for Android packets
* Removed unnecessary else from receiveAuthRequest which was causing
  'An unexpected error occurred' to be continuously printed
* Fixed bug with storing the server token; pointers are no good since
  rx16 is reused