Modify custom function signature generation for state transitions to change argument name "data" to name of event

[matthewadams]

From @gacord23 on September 14, 2016 16:14

This is purely a usability issue.

Given state transition
receives custom checkIn becomes waitingForAssistance sends checkedIn
the generator creates custom function signature
function(causedByEventName,meta,data,done)

Since the term data wasn't meaningful to me, I inadvertently overwrote it in my custom routine. Had the generator used the event name checkIn instead of data, like
function(causedByEventName,meta,checkIn,done)
it may have made things more obvious.

Copied from original issue: SciSpike/yaktor-dsl-xtext#7

[matthewadams]

FYI, started work in branch https://github.com/SciSpike/yaktor-dsl-xtext/tree/7.