add support for referencing commands from another patch in a patch definition

[sean-e]

In the following patch definitions, the hex string used in the momentary patch command duplicates the same strings already defined, since there is no way to refer to the commands of another patch:

<patch name="Delay 1 Hold" device="Axe-Fx" type="toggle" >
	<midiByteString name="A">F0 00 01 74 10 01 09 00 46 00 1B 00 00 00 00 00 04 00 00 44 F7</midiByteString>
</patch>
<patch name="Delay 1 no repeat" device="Axe-Fx" type="toggle" >
	<midiByteString name="A">F0 00 01 74 10 01 09 00 46 00 1B 00 00 00 00 00 00 00 00 40 F7</midiByteString>
</patch>
<patch name="Delay 1 Hold (mom)" device="Axe-Fx" type="momentary" >
	<midiByteString name="A">F0 00 01 74 10 01 09 00 46 00 1B 00 00 00 00 00 04 00 00 44 F7</midiByteString>
	<midiByteString name="B">F0 00 01 74 10 01 09 00 46 00 1B 00 00 00 00 00 00 00 00 40 F7</midiByteString>
</patch>

A workaround for a composite toggle uses the PatchListSequence patch type:

<patch name="Delay 1 Hold (tgl)" device="Axe-Fx" type="patchListSequence" gaplessRestart="1" initialStep="1" >
	<patchListItemName>Delay 1 no repeat</patchListItemName>
	<patchListItemName>Delay 1 Hold</patchListItemName>
</patch>

but it's really just a hack for the same issue. The same hack doesn't make sense for a momentary use.

[sean-e]

Maybe implement by allowing definition of named commands that can be referenced by patches... though then those commands would also need to be supported by imported patches implemented in issue #60