More accurate battery tracking and larger icons

Added the results of my battery profiling as a new more accurate LUT and added some oversampling and "hysteresis" to the battery percentage approximation so that it doesn't fluctuate as wildly with the noisy ADC measurements.

This should provide with a fairly accurate state of charge as much is possible with our setup.

In this change I also increased the size of icons as I find them too hard to really distinguish without good eye sight at the old size.