java: Add Syncbase Ping Pong App

This is the first commit for the syncbase ping pong app.
It has some rough edges but has the basic level of functionality.
- Prepares 2 devices to sync with each other
- Runs the test over |numTimes| iterations to compute an average time
  to send ping and pong between devices.
- Can use the proxy (optionally)

Iteration time (w/o proxy): 425-490ms
Iteration time (w/  proxy): 996-1098ms

Missing features:
- Ability to stop the test in the middle.
- Ability to restart the test or start a second test.
- Ability to run the test again without deleting the app's data through
  the Android settings menu.

Change-Id: Ib1e99af32ba4162bc0613ea0fe609614b2059547
28 files changed