MEGAFLASH: add extra step between selecting erase and actually erasing a slot

[lydon42]

Currently flashing a slot will first check the COR and compare core hardware model to actual hardware model. This requires the user to interact an additional time, as well as giving the opportunity to abort (by RESET).

Selecting erase will directly erase the selected slot without waiting.

• [x] refuse to erase slot 0
• [x] add the extra step to erase
• [x] add option to abort and go back to the main menu (MEGAFLASH)
• [x] remove Flash Inspector from production MEGAFLASH
• [x] removed secret Slot 0 Flashing from production MEGAFLASH

[lydon42]

Upgraded to Release issue, as it concerns slot 0 security.

[lydon42]

Add to jtagflash: Prohibit flashing of non-MEGA65 tagged cores to slot 0