Move `NcchHeader` into a child node

[pleonex]

Is the feature request related to a problem?
To be able to easily access to the NCCH header from generic tools (like SceneGate), it would be better if it's a node as part of the NCCH NodeContainerFormat, instead of just a property.

Describe the solution you'd like
Similar to NitroRom for NDS, put the format of NcchHeader as a node of the NodeContainerFormat generated by Binary2Ncch.

Describe alternatives you've considered
None.

Additional context
None.