back up several/all keys

[tomholub]

• backups should contain multiple keys in single file, all protected by the same pass phrase. It should
  be made clear which keys are getting backed up (but no need to let user choose)

Will create another issue

Originally posted by @tomholub in #955 (comment)

[tomholub]

Let user uncheck keys they don't want to back up

[tomholub]

fix this

      // todo - this would not yet work because currently only backing up first key
      // Xss.sanitizeRender('#module_status .container', '<button class="button long green action_go_manual">BACK UP MY KEY</button>');