Allow precise setting of xverter offset frequencies.

[arekm]

Until now offsets above 1MHz were limited to 1kHz step. I had a need for offset in GHz range, ending up with 360Hz which wasn't possible with 1kHz step.

Replace that step with 1Hz. Maximal xverter offset raised up to 100GHz.

For making life easier when step is >= 1MHz multiply it by 100. This alows fast changing in GHz range while still allowing precise stepping by using 100kHz steps (or less) when needed.

Frequency is kept as 64bit in memory while 48bit in EEPROM, to avoid wasting space (so only one more 16bit area was used for that in a old settings compatible way). 48bit is enough for now.