Support for cloning to T55x7 at different clock rates & 134KHz

* Modified commands (lf em4x):
  em410xwatch      ['h'] -- Watches for EM410x 125/134 kHz tags (option 'h' for 134)
  em410xwrite      <UID> <'0' T5555> <'1' T55x7> [clock rate] -- Write EM410x UID to T5555(Q5) or T55x7 tag, optionally setting clock rate
* Better option checking for em410xwrite & fix for uninitialized vars
* Increased samples from 2000 to 4000 in em410xwatch (2000 is OK for clock=64, but too few for clock=32)