Added USART3 as main USART
Merge commit '3cdfe028c5bc7440941e5ee9c41a888c805f5f2a' into Dev_DISCOVERY

Conflicts:
	STM32F3-Discovery/Fiscopter/MDK-ARM/Fiscopter.uvopt
	STM32F3-Discovery/Fiscopter/src/init.c
	STM32F3-Discovery/Fiscopter/src/stm32f30x_it.c