[#9] Fallback to no related articles if #search throws exception

* E.g. when in dev and no internet, or when the service goes down
* E.g. when the query is malformed

In addition, a job is schedule to report the error to Rollbar, the
current exception handling service.  This is performed asynchronously
using DelayedJob and is written in such a way as to minimise
dependencies on third party libraries.  Only the ReportExceptionJob
needs to be updated in the event that our job or exception handler
changes.
[#9] Set the flash[:info] when rendering unpublished articles
[#9] Render missing article template when access denied.
[#9] flash[:info] messages rendered in the article sidebar.

Includes styling from Twitter bootstrap for alerts. I checked a box
in the custom Bootstrap form for "alerts" and replaced the resulting
bootstrap.css.

Limitations:

Does not include 'close' button to close the flash message.