Add a battery socket connected to the sim808 module

[mohamedboubaker]

When power is turned off, the sim808 loses track of time. This means, when it is turned on again, it will take around 60-90 seconds to acquire a GPS fix. Hooking up the sim808 to a backup battery ensures it always has correct time. Which will speed up the Time To First Fix (TTFF) to around 10-15 seconds.

Add a battery socket or a large capacitor to the VRTC pin.