Create a particle / FlxEmitter editor

[Gama11]

HaxeFlixel/flixel#370

[Ohmnivore]

I'll try to take care of that in the following month, it will definitely reduce the amount of guess-work required for making those emitters.

[ghost]

@Gama11 is this still wanted? If so, what kind of features would we want?

What I'm guessing is a visual editor/code generator for just FlxEmitter parameters, but that seems unnecessary because it's not that hard to customize?

[starry-abyss]

It's wanted at least in one of my projects, also would be useful for jams. Recompilation after each change makes the whole process slow, also not all artists can code.
Basically changing all the values/ranges which are provided by the emitter suffice, plus preview. There is PEX editor, but not all fields get imported (because in HaxeFlixel we don't have all the features 1:1), so it's confusing. Yet I think the export/import approach is more elegant than code generation.
I can do some testing, if you make the editor :-)