Decode User-Name as an IMSI in S13/S13' and S7a/S7d.

Also move the application ID macros into the diameter header file.

Change-Id: Iaca5707c8476d81f50ecdb3aab76be293b5ccfe7
Reviewed-on: https://code.wireshark.org/review/3786
Reviewed-by: Jeff Morriss <jeff.morriss.ws@gmail.com>