Redirected component to UBCodeMirror, if MIME type of document is 'text/x-yaml'.

See https://codemirror.net/mode/yaml/

Checked it in "dev" mode - need your help to tweak eslint, which for some reason tries to check something for this MIME type and causes unwanted error messages. I would ask for help here - to turn ESLint off, if MIME is text/x-yaml.