Added StandardDeviationKeyVal operator and test class.
SPOI-1182 -

Added the Filter operator that can filter the key-value pairs based on the given filter. The keys in the KeyValuePair has to be implement a Filterable interface.

Also added required test cases.
Merge branch 'SPOI-1182'
Merge remote-tracking branch 'upstream/master'
added AbstractStoreInputOperator
corrected comment
Merge branch 'master' of https://github.com/DataTorrent/Malhar
removed duplicates in pom
Merge branch 'master' of https://github.com/DataTorrent/Malhar
Merge branch 'master' of https://github.com/DataTorrent/Malhar
Merge branch 'master' of https://github.com/DataTorrent/Malhar
Merge branch 'dt-0.9.3' into my_master
WEB-49 #fixes Dump Tweets in database on node6.morado.com
Merge branch 'master' of https://github.com/DataTorrent/Malhar
Merge branch 'master' of https://github.com/DataTorrent/Malhar
added package-info.java to lib/db
made most dependencies of contrib optional
removed unnecessary imports
added install script for front
MLHR-771 #close fix the WebSocketOutputOperator reconnect problem