Display device's battery level on status bar

[brentru]

If the user created a new component on Adafruit IO to monitor battery life, the display's battery icon should roughly reflect the current state of the battery (relative to its polling period).

There are four font styles for the battery icon:
LV_SYMBOL_BATTERY_FULL (this is what we currently display), LV_SYMBOL_BATTERY_3, LV_SYMBOL_BATTERY_2, LV_SYMBOL_BATTERY_1

[brentru]

Note that we'll need to use a lvgl timer for this to work properly.