Print sensor speed in Logs
Show toast if no accelerometer
Perform the feature calculation tasks in background

* Doing these on main thread creates a lot of delay
* In future if dataset is too big, fft etc. may take lots of time
Make buffer a ConcurrentLinkedQueue and offer instead of add
Merge remote-tracking branch 'origin/tanjot' into chaudhary

Conflicts:
	app/src/main/java/in/ac/iitb/cse/cartsbusboarding/MainActivity.java