agOrchestralScores: Move content to .tex (basic)

Copy everything from OOo document and make it at least
compilable with lualatex.
Basic formatting already done, but no details and no
content review at all.
agOrchestralScores: first review from Urs

I've mostly reviewed through asking questions in the red
\todo{} items.
I've mainly concentrated on structural elements, taking the
(natural) perspective of a reader who has to learn all that.
In some cases I have done little linguistic changes  but in
general I didn't care for the language so far.

The most important topics at the moment seem to be
- missing explanations (mostly short mentioning is enough)
- material that could be dropped
- explanations that should be moved somewhere else
  to make the structure clearer