Add new magic words: UUID, WIKILANGUAGECODE, USERLANGUAGECODE (ver 3.1.0)

* UUID - generate random UUIDv4 (import from Extension:UUID)
* WIKILANGUAGECODE - Get the RFC 3066 code for this wiki
* USERLANGUAGECODE - Get the RFC 3066 code for current user

Change-Id: I5cdf13e1794d312f005817df87df53d0fbc5df11
Merge "Add new magic words: UUID, WIKILANGUAGECODE, USERLANGUAGECODE (ver 3.1.0)"