Add NES Header editor

[lukexor]

When developing a homebrew game, or when dealing with some unknown ROM it can be helpful to both see and edit the NES header, for example to fix an invalid value or to convert from an iNES header to an NES 2.0 header.

Ref:

• https://www.nesdev.org/wiki/INEShttps://www.nesdev.org/wiki/INES
• https://www.nesdev.org/wiki/NES_2.0