Allow apps to specify an alternative hoodie.js dependency

If you project needs a hoodie.js that is different from the default, you
can now specify an alternate dependency source for `hoodie`.

e.g.:

```
{
  "name": "foo",
  "version": "1.0.1",
  "type": "app",
  "dependencies": {
    "hoodie-server": "~0.8.12",
    "hoodie-plugin-appconfig": "~0.1.0",
    "hoodie-plugin-email": "~0.1.1",
    "hoodie-plugin-users": "0.0.9",
    "hoodie": "git://github.com/hoodiehq/hoodie.js.git"
  },
  "subdomain": "hoodie-foo",
  "domains": [
    "admin.hoodie-foo.jit.su",
    "couch.hoodie-foo.jit.su"
  ],
  "scripts": {
    "start": "node node_modules/hoodie-server/bin/start"
  },
  "hoodie": {
    "plugins": [
      "hoodie-plugin-appconfig",
      "hoodie-plugin-email",
      "hoodie-plugin-users"
    ]
  }
}
```

Closes #164.

* * *

This commit was sponsored by The Hoodie Firm.
You can hire The Hoodie Firm:
http://go.hood.ie/thehoodiefirm
fix spacing
* * *

This commit was sponsored by The Hoodie Firm.
You can hire The Hoodie Firm:
http://go.hood.ie/thehoodiefirm
use hoodie.hoodiejs property in package.json to load custom hoodie.js files
* * *

This commit was sponsored by The Hoodie Firm.
You can hire The Hoodie Firm:
http://go.hood.ie/thehoodiefirm
Merge pull request #164 from hoodiehq/164/feature/load-custom-hoodie.js

load hoodie.js from git / custom branch