[BUGFIX beta] Fix various issues related to ES6 import correctness.

* Remove duplicate imports.
* Ensure that modules do not declare variables with names matching local imports.

These things are currently allowed by the es6-module-transpiler but not by the ES6 spec.
Fix broken build due to unstubbed query params

For Stefan Penner.

/cc @rjackson
Merge pull request #4823 from eventualbuddha/es6-fixes

[BUGFIX beta] Fix various issues related to ES6 import correctness.
simplify EachView context bindings.
remove accidental double assertion o_0)
support itemController all CollectionView's