LCD display too large - filenames are too long

[akc42]

This is basically as a result of leaving space for the long filenames that we are creating. After some throught I believe that the device name only need be a single letter "S" for the Scarlett 2i2 and "B" for the Blue Yeti, we only really need day of month in the date section and the nearest 10 seconds in the time section (we ought to not keep any recording that is less than 10 seconds long) and we don't need the separators between the numerics. So a file made on the YETI microphone at "2020-03-21T07:17:55.134Z" (Date.toISOString()) should produce a filename B2107175.flac