Remove attrs and templating; consolidate to core.clj{s}

## Changes
* Updated ClojureScript, lein-cljsbuild and clojurescript.test dependencies
* Removed all templating-related code (`node`, `deftemplate`, etc.), and removed `dommy.template` ns
* Moved all functions from `dommy.attr` to `dommy.core`
* Renamed `dommy.macros` to `dommy.core`, allowing for:
```clj
(ns foo
  (:require [dommy.core :as dommy :include-macros true]))
```
* Renamed `dommy.core/ancestor-nodes` to `dommy.core/ancestors`
* Added `dommy.core/create-element` and `dommy.core/create-text-node` to make up for removing `node`
* Moved implementation-specific code to `webapp.utils` (for both clj and cljs)

## Todo
* [ ] Check browser support for textContent and classList up front
* [ ] Update readme