Add Intents for starting and stopping logging (for automation)

I have approximately zero experience writing android code, but here is my attempt for issues #32 #71 #105 #108

This adds these custom broadcast intent actions that will start or stop the logging respectively 
com.mendhak.gpslogger.STARTL
com.mendhak.gpslogger.STOPL

I'm not sure if it is the correct way to do it, but for me it allows me to use an app like *Llama* to control the starting and stopping of logging.