Default effects properties were not set, + minor fixes

1.
Default effects properties were not set in the HowlerGlobal object.

The HowlerGlobal object (window.Howler) is instantiated here:
https://github.com/goldfire/howler.js/blob/2.0/src/howler.core.js#L232

But it happends before HowlerGlobal.prototype.init is overrided here:
https://github.com/goldfire/howler.js/blob/2.0/src/plugins/howler.effects.js#L25

Setting default effect properties in the HowlerGlobal.prototype solved the problem.

2.
self.ctx.listener.setOrientation was not set properly on https://github.com/goldfire/howler.js/blob/2.0/src/plugins/howler.effects.js#L105

3.
There was a typo in coneOUterangle

4.
It was not possible to specify only a subset of the panner attributes (maybe it was on purpose ?.. take it or leave it)