pitches.h in main library

I propose having pitches.h in the main library, so they can be used in any sketch without the need of including an extra file in the sketch folder.

Also, it's necessary for the sound effects to work. See commit [1e1a8520f58fa192efd449efe2ce77e96c21251a](https://github.com/arduinoverkstad/BasicEducationShield/commit/1e1a8520f58fa192efd449efe2ce77e96c21251a)

Inspect the library layout and the existing pitches.h referenced by the issue, then review commit 1e1a8520f58fa192efd449efe2ce77e96c21251a to understand how sound effects use it. Done means sketches can use the pitch definitions without copying an extra file, and the sound effects described in that commit work.

Written by the indexing model from the issue text.