CDB-2628 Create Varnish invalidation trigger as HTTP-wide when varnish
http_port is available
Remove TODO comment (table is sent when we don't know which table is
involved
Merge pull request #728 from CartoDB/CDB-2628

CDB-2628 Create Varnish invalidation trigger as HTTP-wide when varnish http_port is available
Revamp Varnish trigger loading task with improvements from load_function
Merge branch 'master' into CDB-3504

Conflicts:
	app/models/user.rb
Reverts extension to version 0.3.6