Muted channel notifications still appear in desktop client menu notification preview

Muted channels should probably not display notifications here. Muted high volume channels will dominate the preview space, making it less useful.

There are lots of interesting, high-volume channels on keybase, and not allowing notifications to be suppressed for these channels has the unfortunate effect of discouraging joining them.

No file, test, or entry point is named. Start by reproducing the desktop client menu notification preview with a muted high-volume channel, then trace the preview's notification filtering. Done means muted-channel notifications no longer occupy the preview while unmuted notifications remain visible.

Written by the indexing model from the issue text.