support copy&paste of lyrics, chord names, figured bass, function marks

[matevz]

In light of #84 we can fully support copy&pasting other music elements than notes in the staff.

For example, steps to copy&paste lyrics (other elements are similar):

1. Select some syllables
2. Ctrl+c
3. Select another lyrics context
4. Click on the syllable where pasting should take place (selected empty syllable is drawn as a dot so user knows something is selected)
5. Ctrl+v
6. The pasted content is inserted at exact position where the syllable was selected. If there are only empty syllables behind, they should be trimmed at the end of the score. Otherwise, they should be added at the end even if the score ended.
7. Shift+Ctrl+v should overwrite the content. In the future, this could open a "Paste special" dialog where user could "clear formatting" (e.g. reset rhythm, reset melody, apply only rhythmical pattern to existing notes etc.) - a similar behavior to LibreOffice.