App Directory schema contains errors

[kriswest]

Area of Issue

[x] App Directory

Issue Description:

The app directory schema is currently failing its test. The example schema at https://github.com/InteropIO/FDC3/blob/544-Desktop-Agent_bridging-Proposal-mk2/src/app-directory/specification/examples/application/fdc3-workbench.json contains error (type should be "web" rather than "browser". However, once corrected the test still won't pass as the details element can't be validated (due to the use of oneOf, where the subschemas overap - this should be anyOf), amongst other errors.

Errors are only returned one at a time due to the encoding in YAML, switching to JSON schema would allow all errors to output at once.

Correct the errors in the App Directory schema and consider switching the encoding to JSON Schema.