Support declarative event filters

[frenchy64]

Adds extension lifecycle cljfx.ext.node/with-event-filter-props to declaratively specify event filters.

Fixes #2

[vlaaad]

Hey, that's a cool example!
I initially thought about having declarative event filters as a map from event type to handler or list of handlers, but since there is a catch-all "any" event, and you can check your event type in handler, this is quite an elegant solution!

I think it should not be an extra-props lifecycle, but instead a part of a core node props in cljfx.fx.node/props. 2 main use cases for extra-props lifecycles are:

• adding props that I missed without having to patch cljfx itself when you are writing an application and just want to get stuff done
• adding synthetic props which are not present on mutable objects as a "place", such as selection props: they are part of selection model, but we pretend it is a part of a list/table because it makes sense.

Event filter feels more like an essential part of a Node in that regard, that's why I think it should be a part of node props.

[frenchy64]

Thanks for your review. I moved the functionality to the :event-filter prop of fx.node.

I initially used an extension lifecycle to make a small library based on the devtools example that "instrumented" your scene automatically by passing it a description of your root node. With this convenient Node prop, perhaps it's better exposing the functionality as an event filter "handler", ie. a library providing the MouseEvent logic in the example.

[frenchy64]

Updated to vector style, and updated example use a pure[r] helper function like I suggested above.

[vlaaad]

Looks good, I'll try it at home one more time later today and hopefully will merge it!

[vlaaad]

Thanks!