Allow for editing document's privacy

- Add PUT to allowed verbs in document resource
- Merge existing raw data with updated data to avoid overwriting fields
 in a map.
- Use prepared query since I couldn't find how to update a list at a
 given index using hayt (waiting to hear from Max Penet about this)

Fixes #544 

Viewing: 
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Editing:
![image](https://cloud.githubusercontent.com/assets/2522010/5458810/a60cbda6-8555-11e4-910d-26755868a824.png)


Our implementation of execute-prepared does this: `(alia/execute (:session this) query opts)` so it only works with a string and doesn't prepare anything. We should probably rename the function or make it do something like this:
``` clojure
(let [prepared-statement (alia/prepare session "select * from users where user_name=?;")]
  (alia/execute session prepared-statement {:values ["frodo"]}))
```
Possibly in a separate PR?