Use .less files directly in MobileFrontend

Uses core .less support from Id052a04dd, I3e06b6d6e, If22afea96 and
I733b53171.

lessphp has some limitations so the .transition() mixin had to be
simplified.

This patch removes references.css and filepage.css in favour of more
generic rules in common.less and enwp.less for references

Change-Id: I068686854ad79e2f63a08d81b1af02f373110613
Merge "Use .less files directly in MobileFrontend"