Move varnish triggers from user tales to CDB_TableMetadata

Closes #197
Jira ref CDB-241
html for new starting page done
Merge branch 'master' into feature/CDB-777
actions for new welcome page
actions for new welcome page
adding specs file
Merge branch 'feature/centralize-varnish-trigger' of git://github.com/strk/cartodb into release/2.5.6
Disable pg_notify on _CDB_TableMetadata_Updated

See https://github.com/CartoDB/cartodb/pull/241
Merge branch 'master' into feature/CDB-777
Remove call to Table#add_python
Remove call to Table#add_python
Update NEWS.md
CDB-777 #resolve - added new videos for empty dashboard tables
Merge remote-tracking branch 'origin/feature/CDB-777' into release/2.5.5
added https to vimeo embeded videos
Merge remote-tracking branch 'origin/feature/CDB-777' into release/2.5.5
Updated NEWS.md