auto-detect base32 vs hex

[fwenzel]

Most of the time, we can probably detect if this is a hex or base32 key. A single character outside the 0-9a-f range makes it a candidate for base32.

[fwenzel]

I am probably 99% right if I autodetect (in that order) "characters in hex range? -> hex; characters in base32 range? -> base32; else? error". There could be outliers, but they would be extremely rare.

For those rare edge cases, we probably want a dropdown for "key encoding:" that defaults to auto and can be switched to base32 or hex if needed.