Develop fw 173

There are three main modification about this pull request.

1. Using HSI clock as system clock source, instead of HSE clock. This will reduce the time duration for re-configuring system clock when wake up from sleep mode.

2. I defined three modes, RUN_MODE, STOP_MODE, and SLEEP MODE and ieee802154e timing for three modes. We used STOP_MODE before, which can acheive lowest power consumption. 

3. I changed it to SLEEP_MODE  instead of STOP_MODE of stm32. With SLEEP_MODE, stm32 can be waken up by uart interrupt, which make "toggle" button in OpenVisuallizer available. However SLEEP_MODE will cost more power than STOP_MODE

4. delete some comments and some unused functions for stm32.