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 'master' of https://github.com/DataTorrent/Malhar
added package-info.java to lib/db
made most dependencies of contrib optional
removed unnecessary imports
added some comments
Merge branch 'master' of https://github.com/DataTorrent/Malhar

Conflicts:
	contrib/pom.xml
MLHR-786 #resolve
1. Added transaction unit test
2. Separate operatorStore and testStore in unit test
3. Fixed redis operator in transaction mode
MLHR-786 #resolve
1. Added transaction unit test
2. Separate operatorStore and testStore in unit test
3. Fixed redis operator in transaction mode
Merge branch 'master' of https://github.com/DataTorrent/Malhar

Conflicts:
	library/src/main/java/com/datatorrent/lib/db/AbstractTransactionableStoreOutputOperator.java
	library/src/test/java/com/datatorrent/lib/db/TransactionableKeyValueStoreOperatorTest.java
Merge branch 'master' of https://github.com/DataTorrent/Malhar
Merge branch 'master' of https://github.com/DataTorrent/Malhar
Demo guide for Pi application. #MLHR-915
Demo guide for PiCalculator demo application. #MLHR-915