Syntactic sugar for sum, min, and max aggregations

This closes #7
[FLINK-957] Throw meaningful warnings and exceptions upon incorrect use of delta iterations.
Added Version and Revision of Stratosphere in Webinterface

https://issues.apache.org/jira/browse/FLINK-946

![bildschirmfoto 2014-06-20 um 14 43 26](https://cloud.githubusercontent.com/assets/5738978/3340103/82d0485e-f878-11e3-9d15-617102ea40a3.png)

Author: Jonathan <Jonathan@Hasenburg.de>

Closes #30 from JonathanH5/wi_version and squashes the following commits:

f29180a [Jonathan] Added Version and Revision of Stratosphere in Webinterface
The Hadoop Compatibility has been refactored and extended to support the new Java API.
Hadoop Compat pull request clean-up

This closes #32.
Fixes a bug where Thread.currentThread().getContextClassLoader() does not return the user code class loader within object deserialization.
Rework the Taskmanager to a slot based model and remove legacy cloud code

Squashed commit of the following:

  - Post merge cleanup
  - Renamed fractionMemory into memoryFraction.
  - Removed Local and QueueScheduler and replaced it instead with an unified DefaultScheduler.
  - Removed Local and ClusterManager and inserted instead an unified DefaultInstanceManager.
  - Removed connection IDs from execution edges
  - Removed InstanceType, InstanceRequestMap, InstanceTypeDescription, InstanceTypeDescriptionTypeFactory, PendingRequestsMap
  - Fixed problems with test cases.
  - introduced simple slot system for scheduling.
  - Removed subtasks per instance
  - Added registerTaskManager to the JobManager RPC calls. RegisterTaskManager is called only once where the hardware description information is sent.

Add: Merging cloudmodel remove with new network stack
Cleanup of merge with slot-based scheduler branch.
Removed RuntimeEnvironment instantiation from execution graph construction. Removed legacy job vertex classes and input/output tasks.
Added failing behavior to JobManager if it is still in scheduled or created state
New test case: Exception during ExecutionGraph construction in the JobManager
Removed checkConfiguration method from AbstractJobVertex because it is not needed anymore
Replaced Tarjan's algorithm with a simpler depth-first traversal cycle detection algorithm. By doing so, one gets rid off a possible linear time check whether a node is contained in the stack.
Streamlined job graph algorithms to get rid off linear contains operations.
Standardized creation of input and output channels in InputGate and OutputGate. Removed linear contains check in InputGate for channels.
Merge fix to omit input/output registering on JobManager
Rework Invokable Task Hierarchy
Add some options for slot-based scheduling and changed default parallelism to one.
[FLINK-962] Initial import of documentation from website into source code (closes #34)
Add script to merge pull requests
Show version information including commit date in TaskMgr log
Add garbage collector stats to output of TaskManager memory usage debug thread
Revert unintentional change in 1357ea3a40f747e4e51b5b52612323fe55747da7