Added better test to existence of cassandra

Jolokia API doesn't return correct the response status in the http headers.
Because of that, the test for existence fails.

I have changed it to check the Jolokia json response for the status as well.
added null check to RE for mbeans type
fixed wrongly displayed type name:
added basic tomcat folder
added a test for tomcat's existence
added api to retreive tomcat threads graphs
added simple graphbox to show tomcat threads graphs
added tomcat pagehandler:
added /dashboard/tomcat route:
added all new tomcat related files to makefile:
added tab for tomcat
removed debugging lines:
added simple derivative plot helper class
added api for tomcat requests graphs
added tomcat requests graph box
added the tomcat requests graphobx to tomcat's pagehandler
added transformation of derivativeGraph to normal array in tomcat/requests api
derivativePlot now checks that timestamp is in expected format
Added strict type check to lastValue

The DerivativePlot#add method was checking for the existence of a previous value.
if there is non, you can calculate the derivative, so you skip it.
When the check was for loose types, and the first value of the plot was 0,
the plot will never render.
Changed the check to a strict one against null and the plots work again.
added api layer for session per context graphs