This is the initial work of SPARK-6939. Not yet ready for code review. Here are the screenshots:

![graph1](https://cloud.githubusercontent.com/assets/1000778/7165766/465942e0-e3dc-11e4-9b05-c184b09d75dc.png)

![graph2](https://cloud.githubusercontent.com/assets/1000778/7165779/53f13f34-e3dc-11e4-8714-a4a75b7e09ff.png)

TODOs:
- [x] Display more information on mouse hover
- [x] Align the timeline and distribution graphs
- [x] Clean up the codes

Author: zsxwing <zsxwing@gmail.com>

Closes #5533 from zsxwing/SPARK-6939 and squashes the following commits:

9f7cd19 [zsxwing] Merge branch 'master' into SPARK-6939
deacc3f [zsxwing] Remove unused import
cd03424 [zsxwing] Fix .rat-excludes
70cc87d [zsxwing] Streaming Scheduling Delay => Scheduling Delay
d457277 [zsxwing] Fix UIUtils in BatchPage
b3f303e [zsxwing] Add comments for unclear classes and methods
ff0bff8 [zsxwing] Make InputDStream.name private[streaming]
cc392c5 [zsxwing] Merge branch 'master' into SPARK-6939
e275e23 [zsxwing] Move time related methods to Streaming's UIUtils
d5d86f6 [zsxwing] Fix incorrect lastErrorTime
3be4b7a [zsxwing] Use InputInfo
b50fa32 [zsxwing] Jump to the batch page when clicking a point in the timeline graphs
203605d [zsxwing] Merge branch 'master' into SPARK-6939
74307cf [zsxwing] Reuse the data for histogram graphs to reduce the page size
2586916 [zsxwing] Merge branch 'master' into SPARK-6939
70d8533 [zsxwing] Remove BatchInfo.numRecords and a few renames
7bbdc0a [zsxwing] Hide the receiver sub table if no receiver
a2972e9 [zsxwing] Add some ui tests for StreamingPage
fd03ad0 [zsxwing] Add a test to verify no memory leak
4a8f886 [zsxwing] Merge branch 'master' into SPARK-6939
18607a1 [zsxwing] Merge branch 'master' into SPARK-6939
d0b0aec [zsxwing] Clean up the codes
a459f49 [zsxwing] Add a dash line to processing time graphs
8e4363c [zsxwing] Prepare for the demo
c81a1ee [zsxwing] Change time unit in the graphs automatically
4c0b43f [zsxwing] Update Streaming UI
04c7500 [zsxwing] Make the server and client use the same timezone
fed8219 [zsxwing] Move the x axis at the top and show a better tooltip
c23ce10 [zsxwing] Make two graphs close
d78672a [zsxwing] Make the X axis use the same range
881c907 [zsxwing] Use histogram for distribution
5688702 [zsxwing] Fix the unit test
ddf741a [zsxwing] Fix the unit test
ad93295 [zsxwing] Remove unnecessary codes
a0458f9 [zsxwing] Clean the codes
b82ed1e [zsxwing] Update the graphs as per comments
dd653a1 [zsxwing] Add timeline and histogram graphs for streaming statistics