MIXER - Select Multiple Mixer Channels

Hello Everyone,

The ability to be able to select multiple mixer channels all at once and be able to perform various actions to this selected group of channels I feel would be a great addition. There are many actions that can be programmed to be used with such a feature.

1.) Routing all channels in this group to a specific channels "send" as explained here
https://github.com/LMMS/lmms/issues/1218

2.) When group is highlighted you can use the hotkey for moving single channels around (hold ALT and use Left and Right arrows) which would move the group as a unit.

3.) You can mute all the channels in this group with one click when all selected.

4.) I believe I read somewhere that someone wanted a "solo" button for each channel to be added, if this feature was ever added you would be able to solo item in that group with one click.

5.) Maybe not greatly needed but when all selected you can link all the volume faders together and all you have to do is use one of them.

6.) You can delete a group all at once.

Sure there are tons more, if anyone has any other suggestions please share.
Thank You

No files, tests, or entry points are named. Start by locating the mixer-channel implementation and existing selection behavior, then narrow the proposal to one specific action. Done should be defined by a focused selection interaction and tests covering that single action.

Written by the indexing model from the issue text.