Make Francois' code available to the apps

[shankari]

Francois has a C++ implementation of the Viterbi algorithm, which we can use for path filtering. It would be nice to run this on the phone so that we have the option of doing more sophisticated initial processing at the phone layer instead of sending all the data to the server.
https://github.com/bellettif/MultimodePIF

Android

Fortunately, it turns out that android does support JNI, so this should not be too complicated.
https://developer.android.com/training/articles/perf-jni.html

So the primary task here is to build a JNI layer on top of Francois' class. You can use the same API that he uses for the python layer.

iOS

iOS already uses Objective C (we haven't switched to Swift), so this should be pretty easy. Again, you can use the same API that he uses for the python layer.

Feel free to contact @bellettif if you have questions.