chore(travis): use saucelabs for chrome and firefox tests
chore(travis): fixed tunnel used by Karma on Saucelabs
Revert "feat(Scope): Instrument Scope to use User tags in Dart Obervatory"

This is only reverted because it is not ready for g3v1x.
We will re-apply this when we have the 'ok' to merge it into g3v1x.

This reverts commit c21ac7eaec3fd15bba7a124fdfb3e9680092a0f2.

Conflicts:
	lib/core/scope.dart