New events #2

Custom events mechanism that avoids the frequent context switches present in Backbone.events.
It's more bareboned but significantly faster. Also replace all occurrences of .bind with .on, to make the distinction between Function.prototype.bind() easier.

**This PR contains/is based on the children as array PR**
The relevant commits are the last three:
https://github.com/DieBuche/two.js/commit/66a500d4b00da0b72e870f2ce2c406a6c65e0f84
https://github.com/DieBuche/two.js/commit/89de632e1b6a571e66910329e0ff9d5a492d85b2
https://github.com/DieBuche/two.js/commit/bb3f93765f5028e297bfa3c143a8630c3b35560f