Integration of HDFS connector
wip
Added operator compactification of linear chains
Introducing the first version of iterations, respectively reexecutable topologies
wip
wip
Merge branch 'develop-iterations-runtime' into develop

Conflicts:
	aura-core/src/main/java/de/tuberlin/aura/core/dataflow/operators/PhysicalOperatorFactory.java
	aura-core/src/main/java/de/tuberlin/aura/core/dataflow/operators/impl/HDFSSinkPhysicalOperator.java
	aura-core/src/main/java/de/tuberlin/aura/core/dataflow/operators/impl/HDFSSourcePhysicalOperator.java
	aura-core/src/main/java/de/tuberlin/aura/core/descriptors/Descriptors.java
	aura-core/src/main/java/de/tuberlin/aura/core/record/RecordWriter.java
	aura-core/src/main/java/de/tuberlin/aura/core/record/RowRecordModel.java
	aura-core/src/main/java/de/tuberlin/aura/core/topology/Topology.java
	aura-examples/src/main/java/de/tuberlin/aura/demo/examples/CompactificationTest.java
	aura-examples/src/main/java/de/tuberlin/aura/demo/examples/DataflowTest.java
	aura-examples/src/main/java/de/tuberlin/aura/demo/examples/IterativeDataflowTest.java
	aura-tm/src/main/java/de/tuberlin/aura/drivers/OperatorDriver.java
	aura-wm/src/main/java/de/tuberlin/aura/workloadmanager/TopologyParallelizer.java
	aura-wm/src/main/java/de/tuberlin/aura/workloadmanager/TopologyScheduler.java
Aura cleanup phase...
wip
wip
Introduces Iteration-State via Datasets
Some bugfixes for the iterations runtime
merging iteration runtime to current develop branch -> wip
bug fixes in the iteration runtime
bug fixes in the iteration runtime
merge with lauritz develop
wip
develop merge
pom: Use Hadoop 2.4.1
ArrayLists instead of LinkedLists to store elements in Operators