Fix english typo on message when removing mask.
style: keep lines under 80 characters.

* inc/actions/masquerade.php, inc/actions/calendar.php: only aesthetic changes
to keep lines under 80 characters.
Add link to return to instrument list at top of calendar view.

* inc/actions/calendar.php: create a link to return to instrument list on top
of the calendar, in addition of the link at the bottom of the page. Also cut on
some duplicated code.