Add unassign confirmation to UserDetail page.

[somiaj]

Update the displayed information on the user detail page.

• State how many sets a user is assigned to out of the total number.
• Change the "edit class list data" link to a button.
• Only show the "Assign All sets to Current User" button if the user isn't assigned to all sets, and state the user's name instead of "Current User".
• Remove all the warnings from the page. Add a statement that unchecking the "Assigned" checkbox will unassign a set and cannot be undone.
• Call the table "Available Sets", as it contains more sets than the ones assigned to the user.

Add a confirmation modal that appears whenever a set is unchecked to require confirmation. This also adds a hidden field so the unassign on the server side will only unassign if that hidden field had been updated to true.

Add a check to see if any of the dates were actually changed, and only update the database entry in the case a change was made to avoid unneeded database calls.

There was some logic which I believe was trying to allow a set date to be "0", but it wasn't working, param('x') && param('x') ne '' was being used, which I think was meant to allow "0", so the logic should have been defined param('x') && param('x') ne '', but the method checkDates was already explicitly disallowing a "0" date. Except for the checkDates method, the logic was all simplified to just checking for the truth of param('x'), since "0" was being disallowed in the checkDates check anyways.

Add a hidden save submit button first (if showing the assign all button), so pressing enter in the form will be a save and not an assign all action.