Validate project file

[jmintb]

As an AME user I want to be informed if my project file is invalid. Currently is there are fields included which aren't supported, there are no errors, the fields are just ignored. This is problematic as I might add a field like "secret", which should be "secrets", but the CLI does not inform me of that.

Acceptance criteria:

1. If the yaml can not be passed, an informative error is displayed by the CLI.
2. If the yaml can be passed, but there are extra fields which should not be there, an informative error is displayed to the user by the CLI.
3. The server performs these validations as well, when processing project files directly, for example from git repositories.
4. The user can have validation errors from the server displayed to them through the CLI.