ListApps API does not scale

[jessesuen]

Try attaching the helm repo to a cluster:
https://github.com/helm/charts

Then, using the UI, try to select an app. This will not return in a timely manner, and it causes a ton of GetFile calls to the repo server.

We should rewrite the ListApps API to only return file paths and App types, and not attempt to extract application names or environments from the ksonnet app.yaml. This logic can be performed when selecting a single app.