fix visibility for items show in network & vitals
remove duplicated translations

translations are in config/locales/views/dashboard
use length instead of count to correct count of visible groups

@memberships is an active record relation. With auth! we remove non readable membership, if we now use the active record count, a database COUNT(*) SQL query is performed which will return the number of memberships before we removed them with auth! (active record doesn't now that we removed some memberships)
fix feed visibility for group & owners when feed is not viewable
fix dashboard if public concerto is enable
change permission requirements for vitals links
Merge pull request #1103 from simplysoft/visibility-fixes

Visibility fixes