[FLINK-1246] Add additional debug output to flaky recovery test
[tests] Various stability fixes to tests
[build] Manage version of joda-time to prevent conflicts between dependencies.
[FLINK-1207] Context environments are realized through factories
  - local execution blocking is reset after each run
[FLINK-1237] Add support for custom partitioners
  - Functions: GroupReduce, Reduce, Aggregate on UnsortedGrouping, SortedGrouping,
               Join (Java API & Scala API)
  - Manual partition on DataSet (Java API & Scala API)
  - Distinct operations provide semantic properties for preservation of distinctified fields
  - Tests for pushown (or not pushdown) of custom partitionings and forced rebalancing
  - Tests for GlobalProperties matching of partitionings
  - Caching of generated requested data properties for unary operators

This closes #207
[bin] Remove MaxPermSize parameter for JVM 1.8

This closes #200.
[FLINK-1209] [compiler] Improve error messages when forgetting to close an iteration
[FLINK-1250] [config] [docs] Correct and document config keys for heartbeat intervals and timeouts

This closes #212
deprecated current aggregation code
Test cases and API for new aggregations
ungrouped aggregations
grouped aggregations
missing license headers
moved AggregationUdf into correct package
name the aggregation operator in the DAG
additional tests for aggregation
CountAggregationFunction does not need an input type
documentation updates
license update
fixed test case