added dynamic_cdn_enabled user flag
updated cartodb.js
updated cartodb
updated news
updated cartodb.js
CDB-4434 missed a varnish invalidation
put the flag in the right place
Merge branch 'CDB-4434' of github.com:CartoDB/cartodb into CDB-4434
set to false then the flag is not set (pass test)
Merge pull request #900 from CartoDB/CDB-4434

CDB-4434 adds dynamic_cdn user flag