A "i'm doin stuff' screen

[baconpaul]

Thinking about #1157 we have some actions which are long time on the serial thread but don't need to block the ui.

For instance, loading an entire big SF2 with all its samples

Would be nice if in addition to the synchronous edge at the thingy in #1157 we had a 'doing stuff' screen so

1. src-ui/app/other-screens/doing-stuff
2. messages to open and close it and to send a message to it
3. a guard class for serialization thread which opens and closes it

so then sf2 load could at least say you are doing it and when you are done.

[mkruselj]

Nice UI might be to have a progress throbber in header which you could click then it says what it's doing. like in BWS, say.

[baconpaul]

Ahh I was thinking modal but yes both modes would be lovely

[mkruselj]

Modal might be annoying...

[baconpaul]

I get that, but right now dropping a bitwig multisample onto a part and having nothing happen for 7 seconds is also annoying! So I was thinking of something to indicate loading is happening

We could also replace the select-multi dropdown with a progress-indiciator or a million other things.

But the trick is to get the messages back and forth and hooked up to something, and then we can draw it some way as step one.