Allow arguments to `{{mount}}` template keyword and `mount` routing helper

The following was discussed at the Ember Core Team F2F in January:

The {{mount}} template keyword should allow normal handlebars style hash arguments. The router DSL style should also allow some sort of API to supply parameters too.

Still TBD:

• What API should the mount routing helper support for accepting parameters?
• Are arguments set directly on the engine instance?
• How can an engine declare which properties are writeable?

[villander]

this already solved 🎉 can we close this @dgeb @rwjblue ?

[chadhietala]

My concern is that you could introduce runtime dependencies making tree shaking and lazy loading more difficult.

export default Ember.Component.extend({
  geo: Ember.inject.service('geolocation')
})

{{mount "blog" (hash geo=geo)}}