Provide vscode configs

There are a number of mozilla files that are just python files (e.g. `moz.build`). It would be ideal for these to be highlighted by their relevant syntax highlighter. For example:

```json
// .vscode/settings.json
{
"files.associations": {
"*.jsm": "javascript",
"moz.build": "python",
"moz.configure": "python",
"app.mozbuild": "python",
"Makefile.in": "makefile",
"mozconfig": "shellscript"
}
}
```