Determine which schemas to use based off of priority

[JPinkney]

Signed-off-by: Josh Pinkney [email protected]

What does this PR do?

This PR implements schema priority. The priority level is modeline > settings schema > schema association > schema store, meaning that if you have a modeline in the file then it overrides everything else associated with the file. Likewise, if you have schema set on the file manually through yaml.settings it will override schema associations and the schema store.

What issues does this PR fix or reference?

Is it tested? How?

You can test manually by creating a .travis.yml file. Observe that it is associated with the .travis.yml schema. Then associate a schema manually to .travis.yml

"yaml.schemas": {
    "https://json.schemastore.org/composer": ".travis.yml"
}

and observe that the composer schema is now picked up and the travis schema from the schema store is not

[coveralls]

Coverage increased (+0.2%) to 80.391% when pulling 989ca8f on schema-priority into ce1609d on master.

[ssbarnea]

I was surprised today to observe that the extension decided to wrongly use "phpdeploy" schema from unknown location regardless the fact that I did configure it to use ansible-playbook schema for that file pattern.

I think it should have being obvious that user-configured yaml.schemas in settings.json should take precedence.

Apparently after a while I ended up having two schemas reporting errors for the same file, one configured by me and the surprise one which I do not know how to disable.