uczenie: add tutorials and explanations

In this folder i'll be placing all kinds of LilyPond tutorials,
explanations about musical notation and so on.
merge two "szkolenie*" files and rename them
uczenie: some touchups in lily tutorials
uczenie: delete installation instructions

they are now part of another manual, no need to repeat them.
uczenie: small corrections
rename szkolenie z notacji muzycznej
uczenie: split notation basics into two documents
histoire du tango - begin inputting music
histoire du tango: continue input
histoire du tango: continue input
szablon: delete instrument files

I'm going to change the template a lot and use it for
crowd-engraving scrores for Epifania, so i don't want
these files to clutter the view. They were unused anyway.
szablon/choir.ly - fix indent and rename to chór.ly
szablon: change xMusic.ily + xWords.ily to x.ily

store both music and lyrics of each SATB voice in one included
file (until now it was separated between two files).
Each of these files should be compilable (i.e. processing it
with LilyPond should produce a complete part of that voice,
including lyrics).
szablon: reorganize and simplify
move miscCommands from szablon to snippets
szablon: delete obsolete headers

EpifaniaHeaders2 was very similar to EpifaniaHeaders,
and JanekHeaders didn't contain anything interesting.
add some notes about Epifania style sheet
first draft of custom context definitions
szablon: create predefined choral contexts (choir.ly for Graham)
szablon: no need for \set Staff.. in context definitions