Test JSON language as extension

[aeschli]

• Linux @joaomoreno
• MaxOS @jrieken
• Windows @dbaeumer

The JSON language mode has been moved to an extension. Test that the existing functionality is still working:

• Validation
  • syntax errors
  • with schema validation
• Intellisense
  • with schema
  • without schema
• Hovers
  • with schema
• Formatting
• Outline

When trying out schemas, try the following ways of configuring schemas:
- define schemas in the workbench. Changes to the schemas will retrigger validation
- use schemas from the web (check out http://schemastore.org/json/)
- associate schemas with a $schema property
- associate schemas in the configuration options
(see VSCode docs for more info) https://code.visualstudio.com/docs/languages/json

• test the schemas configured by vscode extensions:
  • bower.json, package.json, project.json, tslint.json, schema-schema (*.schema.json)

Try dependency intellisense and hovers for package names and values for

• package.json
• project.json
• bower.json

Test intellisense and hovers for the settings schemas:

• default, user and workbench settings
• default and user keybinings
• launch.json
• tasks.json
• user snippets

Test the VS code extensions to package.json

• contributes and all other custom properties