Component sendAction code sample

I think that the API evolved and the code sample wasn't adapted, right?
[NICETHING beta] helpful whitespace classNameBindings assert

I've trolled myself many times thinking that
classNameBindings works with a space separated string
(probably because of how bind-attr class="" works).
This should help me never troll myself again.

/cc @ebryn
[BUGFIX beta] Do not deprecate the block form of {{render}}.

Fixes #4221.
[BUGFIX beta] Provide helpful error even if Model isn't found.

Previously, you would receive an error if no model was found
corresponding to the route name that you are in. We were already
providing a nice assertion (which lets the user know that the model hook
wasn't defined and can't be inferred), but immediately have that we
would throw an error because we were still calling `find` on a
non-existent model factory.

This simply short curcuits the `find` call if `modelClass` isn't found.

Conflicts:
	.jshintrc
	Gemfile.lock
[BUGFIX beta] reduceComputed fires observers when invalidating with undefined

Conflicts:
	packages/ember-runtime/tests/computed/reduce_computed_test.js