Frequency of input data for the classifiers should be synchronized

[mpetruska]

Classifier algorithms currently rely on data that were taken at the same sampling frequency. While currently all sensors work at 100Hz, this can change in the future.
Re-sampling can be done:

• on the phone: this has the advantage of better scaling and some preprocessing can be easier done on the phone; disadvantage is the possible limitations of the phone hardware.
• server-side: this has the advantage of the possibility to share code with the classifiers, and other Scala code; disadvantage is that it can scale really bad for many simultaneous exercise sessions.