Added Zihong Cao to CONTRIBUTORS list

[ci skip]
This closes #21
Added configuration subsection in webinterface

Closes #16 (GitHub pull request)
Also closes FLINK-919
New Webclient

This closes #15
and FLINK-711
Fixed error messages in web client
extended plan-dump test for KMeans
Fixed JSON Bug for some plans.

Signed-off-by: Robert Metzger <metzgerr@web.de>

This closes #23.
Add log info message with memory usage after TaskManager startup finished.

This commit also introduces a logging thread, which repeatedly logs the
memory usage. It can be configured via:
    - 'taskmanager.debug.memory.startLogThread' (default: false)
    - 'taskmanager.debug.memory.logIntervalMs' (default: 5000)
Merge branch 'master' of https://git-wip-us.apache.org/repos/asf/incubator-flink
[FLINk-941] Place pipeline breakers for SingleInput nodes with broadcast variables, if needed.