Assets cleanup

- Now using rails standard assets pipeline rather than hacking my own
conventions for assets serving.  The drawbacks are increase in js from
170->270kb and same for css. The reason for that, however, is inclusion
of non-minified libraries rather than inclusion of page-specific
scripts. This can be worked upon later.
- The benefits however are many:
-- Easier maintenance
-- Faster assets precompilation
-- Simpler vendor libraries updates
-- Snappier page loads
-- More predictive behavior with turbolinks
-- No more delayed script loading issues
- Added Flamegraph for production (doesn't work on windows)
- Fixed many bugs related to previous migration to Rails 4
- Temporary workaround for a Rails 4 bug which is causing hangs on
browser refresh in staging/production.