Use Ember.Error consistently.

We should use `Ember.Error` throughout the codebase if possible to allow
ourselves the ability to deal with any future issues with how various
browsers handle errors.

Please note: I did not change any instances in `ember-metal` since it is
loaded before `ember-runtime/core` (which is where `Ember.Error` is
defined).

Resolves #3552.

/cc @wagenet