Identify MakeCode hex files via UICR

[microbit-carlos]

We can check if a hex file is MakeCode by looking at the magic number on the UICR. This can then be used by the Python Editor to inform the user.

[microbit-carlos]

As the MakeCode hex files add metadata to RAM after the EoF record the IntelHex library throws an error before microbit-fs is able to run any analysis on the hex file (UICR) data:

There is data after an EOF record at record xxxxx