Initial common devfile library support

[elsony]

Provide an initial set of common libraries that can be used by various tools, e.g. odo, Che, dev console, for interactive with devfile and devfile registry.

This item contains:

1. Devfile parser to allow read and write of devfile (Create common library for devfile read and write #144)
2. Validator to provide validation that cannot be covered by schema validation
   • must be applicable to all tools, i.e. non-tools specific
   • e.g. starterProject cannot have multiple remotes defined
   • consolidate dev workspace & odo validations (Consolidate dev workspace & odo validations #151)
   • define devfile validation rules (define devfile validation rules #229)
3. The specific functions required by the dev console (that is outside of devfile 2.0 spec but target for devfile 2.1 spec)
4. Devfile registry access for devfile discovery within the registry
5. Index.json parser for accessing devfile info in a registry