JSFX: current track

[rdhoore108]

* Request

Kindly provide a "special variable" that gives us the number of the track on which the FX is applied

* Benefit

We can use it to index gmem

* Reason

Now we need to use a "slider" to tell the script which track the FX is on, while I'm sure you guys know better than anyone what track it's on.

* Implementation Suggestion

You might call the variable track_num or whatever you like

* Extra comments

Thank you!