Use labels for action keys options
Imageshack plugin fix.
Finish extension i18n localization support.

* English localization was already started for some messages in
   _locales/en/messages.json. All messages used by the extension
    are now in there (except console output).

* Hz.localizeHtml does that by checking all node that belong to
  the class 'localized-msg'. They should contain the attribute 'msg',
  which is the message id for the localization. Their localized
  message will then be written into the node, also on updates on '[msg]'.

* Most of the options page is now js generated. It contained many
  repeating tags, like checkboxes with a description. This repetition
  can be better represented in js.