* Fixed bug with students search
* Documentation for Model_Student
* Utility function Arr::groupBy()

Simplified methods. If you want to group elements by any key, write ->as_array('key').

Separated logic and representation, removed unused functions, duplicates

Usage: $this->user->Faculty->ID or $this->user->Faculty->getDisciplines()

* Moved some static methods to Factory model
* Removed unused param $teacherID
* Assertion checks moved to models

Use RusLang::tr() function instead.

Field Model_Factory::ID came public, new method getStudents() added.
Renamed Model_Students::searchStudents() to search(); removed duplicate method NotAttendingDiscipline().

1) fix Rating Model
2) sql CreateSubject: restore expected behavior (see todo in commit "Refactoring of subjects upload page" 19.06.15)
3) refactor and disable JavaAuth (see todo)

Not all servers detect HTTP_X_REQUESTED_WITH header.
And now it is possible to load excel files.

Default faculty was not defined by default.