Rewrite class attributes on components

[jacojoubert]

Instead of doing:

{{ui-component class="ui-select--default"}}

we should be able to do

{{ui-component class=":component"}}

[ebryn]

Hmm, can you explain the use case?

[jacojoubert]

There is an inconsistency when you use classes with 3rd party components. Take a look at

untitled-ui/addon/templates/components/ui-select--default.hbs

Line 2 in e69115c

class="ui-select--default"

[ianstarz]

Blocked by rewriters improvements; will have to look at recursing into mustache statements.

[ebryn]

Closing in favor of #53, let's make sure this is covered by that work.