Rework build/logs rendering using React.js

This should improve performance when rendering long logs. It also adds
some structure in place for JS that might come in handy as a pattern
later, should we decide to beef up the UI.

 - Uses Fluxxor for modeling the "Flux" architecture
   - LogStore backed by the already existing SSE infrastructure
 - Uses [immutable](https://github.com/facebook/immutable-js) to hold data in memory. This gives us fast comparisons of long lists of log lines improving the render time greatly.
 - JS packages managed with npm `npm install` on the `web/javascript` directory
 should install all you need. `packages.json` manages all the
 dependencies.
 - Uses gulp for js/jsx compilation
   - Browserify for `require('...')` goodness
   - Few other gulp plugins to make js compilation happen
   - On the `web/javascript/` directory:
     - `gulp build`: builds assets (development)
     - `gulp watch`: builds assets (development), watching for changes
     - `NODE_ENV=production gulp build`:
       builds assets (production: uglify)

Potential drawbacks:

 - We now emit events to the renderers [on a timer](https://github.com/luan/atc/blob/a1093987226d261164bc33a5d6d6179aa497db8a/web/javascript/stores.js#L6) (300ms - `EMIT_INTERVAL`) - this might make the build a little less, ironically, reactive to events coming from SSE.