use bluebird as promise library

I would prefer bluebird for the following reason:

- It allows long stack traces. See below
- It is super fast (see http://spion.github.io/posts/why-i-am-switching-to-promises.html)
- It is de facto replacing Q and when as the standard promises library
- It has a good amount of additional functions, such as .catch(), .all(), .race(), etc.

The main reason here are definitely the support of long stack traces. After requiring bluebird, the developer can call ```Promise.longStackTraces()``` to go from this
```
Trace: [TypeError: Cannot read property 'executexxx' of undefined]
    at xxx\src\grabbers\index.coffee:43:16
    at Object._onImmediate (xxx\node_modules\sequelize\node_modules\promise\core.js:34:15)
    at processImmediate [as _immediateCallback] (timers.js:327:15)
```
to this
```
TypeError: Cannot read property 'executexxx' of undefined
    at module.exports.checkxxx (xxx\src\grabbers\IS24Grabber.coffee:31:27)
From previous event:
    at new Promise (xxx\node_modules\bluebird\js\main\promise.js:92:37)
    at module.exports.CustomEventEmitter.then (xxx\node_modules\sequelize\lib\emitters\custom-event-emitter.js:94:12)
    at Object.module.exports.findxxx (xxx\src\grabbers\index.coffee:67:5)
    at Object.module.exports.grabxxx (xxx\src\grabbers\index.coffee:47:7)
    at Object.xxx (xxx\src\app.coffee:36:11)
    at Object.xxx (xxx\src\app.coffee:1)
    at Module._compile (module.js:449:26)
    at Object.Module._extensions..js (module.js:467:10)
```

bluebird is of course compliant with the promises/A+ standard and the test suite passes just as before. I use it in all of my production code and would love to see it being use here, as well!