The devfile website should support hosting multiple devfile schemas

[johnmcollier]

Currently the https://devfile.github.io/ website hosts the latest schema generated from master in this repo (and synced to devfile/docs via a CI job).

As part of #150, upon each release, we'll be syncing each new released schema and a schema pointing to the latest stable version over to the website as well.

To support this, the devfile website should support hosting multiple devfile schemas, and should (preferably) default to the latest stable version of the schema that's been published. There should also be an option to toggle between versions of the devfile schema for viewing (e.g. latest, stable, 2.1, 2.0, etc)

[elsony]

We may want to rename latest to something like nightly to make it clear that it is a WIP version.

[mmulholla]

all done.