- Login filtering
- Complex enter key behaviour
- Process loading icon

Client js tried to get (incorrectly) discipline id from URL and got error at the server side.

See `discipline/666/teachers` page.

Ternary operator is left-associated in PHP (right in C++), so we have:
    (...) ? one : second;

I have put an extra braces to improve the evaluation order.

Look at office/ page

it-lab/grade#29 (comment 111)

* Integration of drag-drop zone
* Some examples about new file structure

* Integration of drag-drop zone
* Some examples about new file structure

Server had been returning number of affected rows minus one: either 0, or -1. This value is converted to bool (res == 0), and js displayed an error.