Add support for skip$,orderby$ and limit$

I've added the support for skip$,orderby$ and limit$ api and refactor test to have all them green.
I've also updated the seneca and seneca-store-test version. 
this is going to be super-slow. At the bare-minimum, you need to cache them with a [LRU-cache](http://npm.im/lru-cache), but I think we should do much better that this.
Also, attaching a property to an object can cause some performance problems too, so we might even store the 'visited' thing in its own map.

Moreover, does elements in the array have a an id$ we can use, instead of a JSONification?