Shutting up musical instrument messages

[DarkDaskin]

When playing a musical instrument, it outputs a message every few turns. As a result, the log is cluttered by these messages, so it is easy to miss more important ones.

The easiest way to fix that would be adding a global option Hide musical instrument messages and checking for it in musical_instrument_actor::use, but I am looking for better ways to handle that, so all the work put into designing the instruments would not be deprecated.

Some ideas:

1. Make a new message category for music and implement filtering in the sidebar as well as in the log window. The latter has basic filtering, but there is no way to exclude specific categories.
2. Group the messages, so only the last one is shown. Currently implemented message grouping compares the text, but each musical instrument has several random texts, so we need to implement another grouping criteria.