Create C++ mock class and integrate it in the app

[azaat]

• Create a basic C++ class, which has the method taking two IMU data files and returning some constant number

• Integrate it instead of doGyroSyncOnServer in ImuTimeSync.java

• This could be useful to test out integration of C++ methods in Android project (to make sure there will be no problems with the real algo, also to be able to reuse this setup with real algorithm)