RM#3508 rev 1

[Tomáš Hrčka]

I have added before filter to check if request is json and then invalidate 
session manually.
Regular user activity is handled by activerecord session store timeout option. 
This patch may need another revision 
to set the session timeout time in configuration file, but right now I am not 
sure where it should be.
There is another option to make sure all sesions ale expired is to create 
delayed_job
 job for periodicaly checking SessionEntity table.