Helpful methods

This does a few little things:

* Better handling of get/set rels on non-persisted nodes
This allows you to do something like this without getting a Cypher Response error:
```ruby
student = Student.new
student.lessons.count
```
Associations will return an empty, frozen array if `has_many` and nil if `has_one`. Trying to create relationships on non-persisted nodes will still raise errors but this will keep Views (particularly forms that are shared between `new` and `edit` actions) from freaking out.

* Fix pagination
I noticed last night that calling `count` on a query was returning the entire result and then counting in Ruby. Brian put in the fix but pagination needs this or it crashes. Performance is vastly improved, Neo4j-will_paginate's performance is awesome.

* Better `include?` method
Similar to `count`, this makes `include?` check for the presence of a node on the server rather than returning the query and checking on the enumerable.