i18n: Allow multiple translations of "Open"

The software defines at least three contexts for the phrase "Open"

  * The name of a ticket queue (Open tickets)
  * A status of a ticket (Open / Closed)
  * An action to be performed (Open a ticket)

References:
(Crowdin login required)
http://i18n.osticket.com/translate/osticket-official/148/enus-de#2915