CLAP plugin host integration 1

[emrum]

only minor testing yet, but for the CLAP plugins, sound and GUI seem to be working well so far.

[spamatica]

Hi there, I see you closed the pull request. I just wanted to say that if it was due to lack of response I feel you, there are very few people working on MusE...
Now, I haven't had the opportunity to look at the code but I think the feature is very interesting and it would be great if we could get it merged.

[emrum]

yes, thank you.
the feature also got integrated into this branch:
#1329
, thus i decided to close this other one.

you can download that branch and check if everything works well.
i think, there are some required fixes and useful additions in it.