Many small improvements:
- Gpio now as constexpr,
- convert spaces to tabs in spi interface,
- add initialize<baudrate> method to uart interface,
- add check for startPin to AVR GpioPort specialisation,
- Fix UartSpi DataOrder for non-extended IPs.
UI: Convert ButtonGroup to new coding style.
UI: LED: Convert pointers to references for easier code.
Remove unnecessary virtual method declarations in ui::Led class.