Change the type of variable "boot_time" to uint32_t
Create function "get_boot_time"
Rename the typedef "vehicle_data_t" to "global_data_t"
FIx the implicit warning of function "init_vehicle_data"
Merge branch 'mavlink' into global_data

Conflicts:
	program/system/communication.c
	program/system/global.c
Save the boot time in the global data list