Add functionality for Actical, Fitbit and Philips Health Band

[vincentvanhees]

I am adding this functionality for a client. The number of 'external epoch data' formats is growing and the code is all in convertEpochData.R, so I think it is time to start splitting this function and moving the essential parts to GGIRread. First step may be to do the split inside GGIR but in a way that these splitted functions can be migrated to GGIRread later on.