Builder needs some modernization

[marcoscaceres]

We do a bunch of stuff in the builder that is now natively supported by r.js. We should just use r.js to do the following:

• always default to uglyfy2.
• Allow uglyfy2 to compress (with safe options).
• use insertRequire instead of manually including require(["..."]) in the boilerplate.
• remove boilerplate method, and use wrap: option instead.

[marcoscaceres]

Modernized it a bit - now using uglyfy3. Eventually, want to move to webpack #1129