* Set bootloader to stm32-dfu for STM32F303
* Set bootloader to stm32-dfu for STM32F0x2
* Set bootloader to stm32-dfu for STM32F4x1
* Set bootloader to stm32duino for sowbug
* Delete redundant bootloader_defs headers
* Add some missing MCU name comments
* Move APM32 dfu-suffix overrides underneath bootloader
* Remove redundant STM32_BOOTLOADER_ADDRESS defines/rules
* refactor keyboards using ST_STM32F072B_DISCOVERY to use 'MCU = STM32F072'
* refactor keyboards using GENERIC_STM32_F042X6 to use 'MCU = STM32F042'
* refactor keyboards using GENERIC_STM32_F103 to use 'MCU = STM32F103'