Contribute schema for bsconfig.json

[kfish610]

VS Code provides a contribution point for json schemas. Using this would avoid the need for a $schema property in the bsconfig.json (which currently is a bit broken, since the schema doesn't allow for a $schema property.....). All that would be necessary is the addition of

"jsonValidation": [
  {
    "fileMatch": ".jshintrc",
    "url": "https://json.schemastore.org/jshintrc"
  }
]

to the contributions.

[chenglou]

Thanks! Added. Though it only works on vscode.

It's kinda sad that "$$schema" isn't recognized while being a pseudo-standard. I think we're gonna keep that key for various starter templates so that other editors can read from it maybe. Can be removed manually easily anyway.