Icons: Add Cellular bars

[earboxer]

Hey, wondering if you're around (haven't gotten through via email, so I'll give github a go). (Your original project doesn't have any mailing lists linked: if you're interested in contributions there as patches, I could do that as well.)

I've been working adapting this for SXMO, so I'll have some more changes coming, which you can see ahead of time at https://git.sr.ht/~earboxer/statusbar