nrf51822: Implement delay module
nrf51822/log: Replace nrf_delay module by delay
examples/ll-scanner: Replace nrf_delay module by delay
nrf51822: Remove nrf_delay.c from sources list
nrf51822: Implement uart module
nrf51822/log: Replace app_uart module by uart
nrf51822: Remove app_uart.c and its dependencies from sources list