Revert "Rename Meteor.Collection -> Mongo.Collection"

This reverts commit 96952dda2b8b2bd5df8cf4556ebd8da2a535203a.

Conflicts:
	packages/ddp/livedata_tests.js
	packages/minimongo/minimongo.js
	packages/mongo/collection.js
	packages/mongo/mongo_driver.js
	packages/mongo/mongo_livedata_tests.js
	packages/mongo/oplog_tests.js
	packages/reactive-dict/reactive-dict.js
	packages/session/session_tests.js
	tools/auth.js
Rename Meteor.Collection to Mongo.Collection again
Add backcompat
Add link redirect