feature: give feel of realtime heart rate

[shashankRanaNW]

To give a feel of realtime heart data, implement rolling analysis of heart rate. That is, take heart rate data for 20s, and after each 2s, remove the oldest 2s from the heart rate analysis queue, but the newest 2s into it, and calculate the heart rate. 20s and 2s are just examples.

bonus feature:

• Increment the size of heart rate queue from 6s to eventually 20s, there by not making the user to wait for 20s for first heart rate.
• Make 2 different heart rate tracks(arrays/ whatever database) in the app, one for above written heart rate measurement, one for longer term(1min to 2min 's ECG data) for heart rate metrics which can be calculated from aditya bhat 's heartpy code