refs #7608 - i18n fixes, tests, use POST for action + only display link if authed

* i18n interpolation wasn't right (was inside _() instead out of outside) and one word was being passed in as a URL parameter, so that's now hardcoded in the string so it can be translated in full.
* Rewrote the strings a bit to improve the English.
* Changed method to POST as it modifies data and switched URL helper to hide links when unsuitable.
I'm not aware having this UI flow either (where in some cases we have a
drop down and in others we dont).

IMHO, the real solution in this particular case is to revert this and
enable checkboxes with multi action on parameters (in edit).