Add proj4 to package.json
Allow Proj4js to be loaded after OpenLayers
Update to use the documented Proj4js 2.2.x API
Simplify ol.proj.addCoordinateTransforms

Equivalent projections do not need to be handled here, and the forward
and inverse functions can be function arguments instead of being nested
in an object literal.
Use proj4.js from node_modules/ instead of copying it to build/