ES6 modules -> ES5 globals transpilation with sourcemaps

- :warning:  *entering prototyping area* :skull: 
- run `grunt es5` to get sources transpiled to AMD and then concatenated 
- that all with appropriate sourcemaps generated alongside
- so far `core`, `ajax`, `authorization` and `oauth` works
- the AeroGear global is exposed as it ever was, authorization.html test leverages that 

Demo here:
- https://rawgit.com/lfryc/aerogear-js/es6-core-dist/tests/unit/authorization/authorization.html
btw I will pre-fill this option and `karma.options.moduleTranspiler.options.paths` in a new task, so that it won't be so fragile ;-)