Get the Android app building and linking to native libraries.

Changes:
  * Update `build.sh` to properly build, link, and install
    cross-compiled libraries.
  * Update `.gitignore` to ignore generated build files and git repos.
  * Update `update.sh` to clone libuuid.
  * Update `Android.mk` to tell the NDK to link with the generated
    libraries
  * Add the JNI interface.

TODO:
  * Update docs.
  * Remove hard-coded paths to "/home/shancat/".
  * Fix the app crashing on toggle.
  * Update Travis build script.

Signed-off-by: Shannen Saez <shannenlaptop@gmail.com>
Remove hardcoded "/home/shancat".

Requires that a user has set the TOOLCHAIN variable correctly.

Signed-off-by: Shannen Saez <shannenlaptop@gmail.com>
Update Travis build.

Builds and uses the NDK toolchain.

Signed-off-by: Shannen Saez <shannenlaptop@gmail.com>
Send/receive new files

- uses simple and stupid strategy of sending whole file as single frame
- will work for demo, sending photos
- for real work we need to use credit-based chunking as in FILEMQ