* 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

Default faculty was not defined by default.

Russian constants are moved to twig & RusLang modules.
Functions were renamed to Semesters::load($id) & Semesters::loadAll().

/coursework/create — create new coursework
/discipline/create — create new discipline
/discipline/127 & /discipline/127/structure — edit the discipline with id 127
/discipline/127/students — edit the list of attached to discipline students

Moved duplicate code to before() method, some other refactorings.