reenabled ghost tables

there are some things to review:
- how the ghost tables task is launched
- will it work with multiuser
- the user specs where not working
fixed search_for_cartodbfied_tables when the user has no tables
fixed, really
fixed get_cartodbfied_tables when there is not tables in user metadata database
fixed ruby lovely thing
fixed wrong condition
fixed spec
fixed specs
fixed specs
fixed when job is null
fixed resque checks
don't launch a migration when a table is registered
do ghost tables checks when the database has no tables
rename the visualization when the table is renamed
CDB-4407 importer stats test skeleton
CDB-4407 CartodbStatus naming refactor
CDB-4407 test duplication refactor
CDB-4407 spec naming refactor
CDB-4407 statusd timing test at runner with multiple sources
CDB-4407 statsd timing