v0.8.66

Found while the FM/DAB radio plugin was being developed: a station received in mono had no icon.

• An icon for FM in mono, and icons by signal level for FM and DAB. The radio plugin names what plays as FM or DAB with its signal after it, five dots of which the filled ones count (FM ◦◦●●● is 3 of 5), and says a mono station with one channel. The icon for what plays is now looked for under the most telling name first and the plainest last: fm_mono_3, fm_mono, fm_3, fm, and the type's own name; the first found is drawn. The plugin brings the set: fm_0 to fm_5 and dab_0 to dab_5 with the signal as bars beside the letters, fm_mono_0 to fm_mono_5 with MONO under the letters, and fm_mono without bars. A theme brings its own under the same names in its format-icons folder, as before, and may bring only some: a theme with fm_mono.svg and no levels shows it at every level.
• A type the player reports with one channel is looked for under its _mono name first, whatever the source; where no such icon is there the plain one shows, so nothing changes for a mono file.
• The display reads the state's channels.