Add mongodb block

Tested on twitter-trands width ``configs/development/env.js``

````js
/* ... */

module.exports = {
   /* ... */
    mongoCredentials: {
        host: 'localhost', // optional, default is localhost
        port: 27017, // optional, default is 27017
        database: 'test',
        username: '', // optional
        password: '' // optional
    }
};
````

and ``lib/blocks/includes/posts.js``

````js
module.exports = {
    call : 'mongodb',
    params : {
        credentials: require('../../config').get('env').mongoCredentials,
        collection: 'Post',
        operation: 'find', // optional, default is find, tested with find, findOne, insert, update, remove
        query: {} // optional, default is {}
    }
};
````