Add `ember install` action

[makepanic]

Similar to ng add action in the latest angular plugin, we could add that for ember install:

Their source is at https://github.com/JetBrains/intellij-plugins/blob/master/AngularJS/src/org/angularjs/cli/actions/AngularCliAddDependencyAction.java

[makepanic]

I got a prototype of this working using emberobserver as datasource.

There are some open questions I have:

• can we copy the ng approach of having a list of addons in the repo?

We could do the same by using the emberobserver autocomplete data and keep it in the repo.

This allows us to use github infrastructure (and not add additional load to emberobserver) while being in control over the data. We could even strip the dataset and remove unneeded data to reduce download size.