Backend: Fixed bugs with addressing nonexistent variable.

Switching from module-level event handle to global event handler
caused some problems with using variables that no longer exist.
Contact form: Add option for silent AJAX submission.
Collection: Page control: Make swich animation work from CSS.

PageControl will add `visible` class to pages and controls connected
to it instead of animating showing/hiding manually.
Backend: User manager: Fix issue with changing password.