Fixes #541
Merge pull request #543 from herby/gh-541

Fixes #541
using for: self transportType to create package handler
using for: LegacvPackageHandler extracted
commitChannels extracted
refactored default commit path per transport type
commit-related things are all in through *Importer-Exporter
DRYing through Package>>transport
Renamed tests.

They in fact do not do anything interesting with Package.
They test functionality of LegacyPackageHandler.

The tests should be moved. They are not Kernel tests.
Merge branch 'package-loader-etc' into requirejs-wip

Conflicts:
	js/Importer-Exporter.js