Add setting to disable editor services

[glennsarti]

The internal setting to disable editor services was created in #442 (https://github.com/lingua-pupuli/puppet-vscode/blob/master/src/settings.ts#L44)

However there was never a setting added to package.json to allow a user to actually set it.
i.e "puppet.editorService.enabled": false, complains the setting doesn't exist