add iq capture commands for gqrx

[mhassell]

Related to a request on GQRX, I added logic for capturing the IQ part of the signal and not just the audio.

This was tested by connecting GQRX and gpredict, and confirming that when the AOIQ/LOIQ options were checked in the GUI, that an IQ file was produced.

[mhassell]

Converting to draft because of changes being made in gqrx that will impact this PR

[Akira25]

Great draft. As far as I understood, the new commands merged in gqrx are these:

U IQRECORD 1
U IQRECORD 0
u IQRECORD

(see also gqrx-sdr/gqrx#1403 (comment) and gqrx-sdr/gqrx#1142)

I'd find it great to get these command somehow included here.

[mhassell]

Okay, I changed the commands to match the commands that were used in the gqrx branch that was used to allow remote IQ capture. I tested this by compiling the master branch of gqrx and compiling this branch of gpredict. I then found a satellite that was entering view and set up an IQ and audio trigger for that sat. I then confirmed that the IQ file was produced and matched the length of time that the sat was in view. This demonstrates that the U IQRECORD {0|1}commands work and can be set through gpredict to interact with gqrx.