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
 - 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)