See `discipline/666/teachers` page.

Link with name "Back to rating". The bug was caused by editing some routes.

* 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.

1. Discipline models have the direct access to fields, for example: $discipline->subjectName, so you don't have to remember them (press ctrl+space). Improves static code analysis. Also, if you make a mismatch, ErrorException will be thrown — this is the most important improvement.

2. There are some operations on disciplines (attach new teacher, transfer discipline to another teacher, an so on), so you can use them: $discipline->attachTeacher(53).

3. Discipline model has array access operators, so you must not convert instances with toArray() method. A common way is:

/* PHP */
$d = Model_Discipline::load($id);
$d['extraField'] = 127;
$twig->Discipline = $d;  // is ok, cause $d is like an array

/* Twig */
{{ Discipline.extraField }}   // call $d->offsetGet('extraField') method

4. Models Faculty, Student, Teachers and Groups have `getDisciplines()` method, and an array of Model_Discipline will be returned.

5. We use camelCase for all fields: in twig, on the PHP level and also in the database.