convert all models into JSDoc @typedef

[millermedeiros]

right now the models doesn't do anything, they just copy arbitrary properties on the constructor. It doesn't really make a lot of sense to have constructors that doesn't do anything, what we really need is an "interface".

I recommend a simple JSDoc @typedef instead:

/**
 * @typedef {Object} DAVObject
 * @property {Object} data
 * @property {string} etag
 * @property {string} url
 */

see #50

[lambdabaa]

I agree!