add Russian (Student) layout

[Zolax9]

#573
adds a variant of the Russian layout that is used in GBoard and other keyboards for learners of the Russian language (more info and screenshots in the mentioned issue). please review the commit as I'm not entirely sure if I've implemented it correctly!

many thanks!

E̶D̶I̶T̶:̶ ̶̶̶d̶o̶ ̶n̶o̶t̶ ̶m̶e̶r̶g̶e̶ ̶y̶e̶t̶̶̶ ̶a̶s̶ ̶t̶h̶e̶r̶e̶ ̶i̶s̶ ̶a̶n̶ ̶i̶s̶s̶u̶e̶ ̶w̶i̶t̶h̶ ̶o̶n̶e̶ ̶o̶f̶ ̶t̶h̶e̶ ̶l̶e̶t̶t̶e̶r̶s̶ ̶i̶n̶ ̶t̶h̶e̶ ̶l̶a̶y̶o̶u̶t̶ ̶b̶e̶i̶n̶g̶ ̶d̶i̶s̶c̶u̶s̶s̶e̶d̶ ̶i̶n̶ ̶t̶h̶e̶ ̶r̶e̶l̶a̶t̶e̶d̶ ̶i̶s̶s̶u̶e̶.̶

EDIT2: the issue has been fixed and the layout name was changed from "Russian (Students)" to "Russian (Student)" as a better translation of the layout's name derived from GBoard

[Helium314]

The subtypeId must be unique, see layouts.md.

Further, is it necessary to have the popup keys for е and ь?

Otherwise it should be good.

[Zolax9]

The subtypeId must be unique, see layouts.md.

oh, my bad. changed to a unique hex number

Further, is it necessary to have the popup keys for е and ь?

I was not aware that they were already pop-up keys for the Russian language. thanks, fixed as well!