Semi-experimental refactoring

This pull request introduces two primary changes: using [prismatic/om-tools](https://github.com/prismatic/om-tools) for less boilterplate-y component definition and a new `community.util.transform` utility for better model data transforms.

## prismatic/om-tools

The biggest thing this gives us is `defcomponent`, which is a bit of sugar on top of the usual `reify` business. However, this also affords us a bit more flexibility going forward due to its [mixin support](https://github.com/Prismatic/om-tools#mixin-tools). Mixins should allow us to better compose things like the autocomplete and resizing textarea behaviors.

I considered simply writing `defcomponent` myself but dismissed it as a waste of time for now because I anticipate wanting mixins very soon.

## community.util.transform

We do some transformations on data that arrives from our API. For instance, users have a `:name` constructed from their `:first-name` and `:last-name`, threads and subforums get a `:slug`, etc. These transformations are mutually recursive as well: a user might have notifications, which may contain a user they were mentioned by and the thread they were mentioned in. This nested data needs to be transformed as well.

`community.util.transform` lets us define data transformers. A transformer is a collection of transforms, and a transform specifies some function that should run on the value of a specific key. Examples:

```clj
(require '[community.util.transform :as t])

(t/transform {:x 1} {:x inc})      ;=> {:x 2}
(t/transform {:y {:x 1}} {:x inc}) ;=> {:y {:x 2}}
(t/transform [{:x 1}] {:x inc})    ;=> [{:x 2}]
```

`deftransformer` and `deftransform` work sort of like `defmulti` and `defmethod`, allowing us to incrementally build up a transformer and providing some sugar to reduce boilerplate.

```clj
(require '[community.util.transform :refer-macros [deftransformer deftransform])

(deftransformer api->model)

(deftransform api->model :user
  {:as user :keys [first-name last-name]}
  (assoc user :name (str first-name " " last-name)))

(api->model {:user {:first-name "Zach" :last-name "Allaun"}})
;;=> {:user {:first-name "Zach" :last-name "Allaun" :name "Zach Allaun"}}

;; except that :user is sometimes :mentioned-by, so we can do the following:
(deftransform api->model [:user :mentioned-by]
  ...)

;; except that sometimes we have a vector of users called :autocomplete-users, so we can do the following:
(deftransform api->model {:single [:user :mentioned-by] :many :autocomplete-users}
  ...)

(api->model :thread
  {:autocomplete-users [{:first-name "z" :last-name "a"} {:first-name "d" :last-name "a"}] ...})
;;=> {:autocomplete-users [{:first-name "z" :last-name "a" :name "z a"} {:first-name "d" :last-name "a" :name "d a"}] ...}
```

Using this to define our transformations drastically reduces boilerplate and prevents us from forgetting to apply a nested transformation, since all applicable transformations are recursively applies automatically.

## Production build warnings

A last thing to note is that these changes introduce the following warning when compiling the production build:

```
Compiling "../app/assets/javascripts/client-prod.js" from ["src"]...
Jun 30, 2014 11:33:47 AM com.google.javascript.jscomp.LoggerErrorManager println
WARNING: /Users/z/dev/community/client/target/cljsbuild-compiler-2/schema/core.js:889: WARNING - References to the global RegExp object prevents optimization of regular expressions.
schema.core.Regex = RegExp;
                    ^

Jun 30, 2014 11:33:47 AM com.google.javascript.jscomp.LoggerErrorManager printSummary
WARNING: 0 error(s), 1 warning(s)
Successfully compiled "../app/assets/javascripts/client-prod.js" in 6.61 seconds.
```

This comes from prismatic/schema (through prismatic/om-tools). I did some research and it isn't anything to worry about. Closure is a very loud compiler, and it warns you whenever it encounters JavaScript that prevents a certain kind of optimization. This doesn't mean the emitted code is incorrect– there are a bunch of micro-optimizations that Closure does that only work if certain things hold true. Most compilers would just quietly not do that optimization, but Closure lets you know.

Prismatic is aware of this warning however, and it'll likely be fixed in a later release.
Transformations happen outside-in, so the `:xs` transformation happens before the `:x` transformation.