Update composer.json

This now specifies a conflict with MW < 1.23. Putting a requirement
for MW >= 1.23 might make more sense, though that has the downside
that one is no longer able to check out the repo and run
"composer update" without installation via MW.

Also updates some links

Change-Id: I5736fde7cbf803c23ec94de6448ad37e9e3e270c