Set chef reconnect rate to 3

I have put the chef retry connection rate down to 3 retries in order to
prevent extreme long page loadings in case of the chef server is gone. I
think it should be enough to retry to connect only 3 times.
Fix UI if chef-server is gone (bnc#865072)

The ticket https://bugzilla.novell.com/show_bug.cgi?id=865072 explains
that crowbar behaves bad if the chef-server is gone and not reachable.

In order to display a better usable error page i have integrated more
exception classes that gets catched by the application controller to
display a proper error page if there are documents not found or the chef
server is gone.
Added a more natural tone to the error pages
Merge pull request #1075 from tboerger/feature/chef-offline

Fix UI if chef-server is gone (bnc#865072)