[BUGFIX beta] SVG support for metal-views

This greatly improves SVG support in metal-view by basing the current
namespace off the contextual element. SVG components like {{somePath
should be viable with this change.
[BUGFIX beta] Use domHelper for setting attributes, allows camelCase attrs
Fixes classNameBindings regression

`classNameBindings` was initialized as an empty array inside `propertiesFromHTMLOptions`
so we could maintain the same shape of the object via this
[PR](https://github.com/emberjs/ember.js/pull/5559).

When the view is [created](https://github.com/emberjs/ember.js/blob/master/packages/ember-views/lib/views/states/in_buffer.js#L38), `options.classNameBindings` is an empty array
and the view gets confused about its classes.

Scumbag @twokul.

Fixes #5660
Merge pull request #5666 from twokul/class-name-bindings

Fixes classNameBindings regression
[DOC] make run.later return val consistent with other run methods
Merge pull request #5675 from carpeliam/master

make run.later return val consistent with other run methods
Merge pull request #5654 from mixonic/metal-views-namespaces

[BUGFIX beta] SVG support for metal-views