Add JSPM dependency support

Greets,

I like this project! I'm curious how hard it would be to add JSPM (www.jspm.io) support. It's a package manager on the edge of popularity and having increasing uptake. While it manages / installs NPM and Github repos it would be awesome to add to David support for NPM packages. Below is the package.json for one of my repos (Backbone-ES6):

```
{
"name": "backbone-es6",
"version": "0.1.0",
"homepage": "https://github.com/typhonjs/backbone-es6",
"description": "A fork of Backbone converting it to ES6.",
"license": "MIT",
"repository": {
"type": "git",
"url": "https://github.com/typhonjs/backbone-es6/"
},
"bugs": {
"url": "https://github.com/typhonjs/backbone-es6/issues"
},
"jspm": {
"main": "src/ModuleRuntime.js",
"devDependencies": {
"babel": "npm:babel-core@^5.8.25",
"babel-runtime": "npm:babel-runtime@^5.8.25",
"core-js": "npm:core-js@^1.2.1",
"jquery": "npm:jquery@^2.1.4",
"underscore": "npm:underscore@^1.8.3"
}
},
"devDependencies": {
"bluebird": "^2.10.2",
"jspm": "^0.16.13",
"gulp": "^3.9.0",
"gulp-esdoc": "^0.1.0",
"gulp-eslint": "^1.0.0"
}
}
```

As you can see under the `jspm` hash is a `devDependencies` entry. Entries preceded by `npm:` are NPM packages. There can also be a `dependencies` entry as well. If detected I'd imagine David could have additional tabs and badges for JSPM dependencies and JSPM devDependencies listed for a project page.

Extra credit would be supporting Github dependency version checking, but that is a bit much of an ask. NPM packages are preferred in JSPM, so it would be fantastic to see that supported.

I can perhaps take a look, but not immediately, so I'm just throwing out this idea as possible future support / feature to be tracked.

Cheers!