create a 'preprocess' event for table objects

[jwildfire]

The callback should be run at the beginning of the table.draw() function.

Test notes

• No need to feature test.

[jwildfire]

@emorris @samussiah @pburnsdata slotting this in to v1.11.0 since it would make the data flow in the new RAVE heatmap renderer quite a bit easier. I think it's just a couple of lines of code to define the new callback and then run it at the beginning of table.draw().

Just let me know if you'd like me to do a quick PR.

[samussiah]

Is the use case here to avoid adding custom event listeners to controls?

[jwildfire]

yeah, that's definitely one use case, which is especially important if you want to apply the same event listener to several controls. I can imagine others as well.

[dschwentker]

Ne testing needed