Feature/mintlayer pk

[OBorce]

Add new messages in the proto files for Mintlayer coin support, and handlers.

[azarovh]

I wouldn't merge this to master but rather created a separate branch like mintlayer-master and merge features there. This way we can keep it clean and isolated and when we decide to update trezor version we will pull to master and rebase our master. Otherwise it could become a mess very quickly. Makes sense?

One thing to consider is that CI might not work for "our" master.

[ImplOfAnImpl]

As I can see, there are still many FIXMEs and commented lines, so it seems like this is still work-in-progress.

[ImplOfAnImpl]

Probably this should be merged after the relatively trivial comments have been aplied. And the rest can be addressed via separate tasks. But let's create an issue with a list of such tasks, so that they are not lost.

P.S.

1. Some older review comments have not been addressed. Plz make sure all the comments are addressed before merging.
2. The build is broken after the latest rebase.

[ImplOfAnImpl]

This will raise an exception like "ValueError: '1' is not a valid MintlayerChainType" because chain_type is a string.

So, it should be messages.MintlayerChainType(int(chain_type)) instead.

Same for other commands below.

[OBorce]

fixed the CLI to parse the arguments as int

[ImplOfAnImpl]

For bitcoin, they have an address_n field which is used for change outputs. So the device knows when an output is a change one and doesn't show the output confirmation to the user in such a case.
IMO we should behave similarly, because confirming change outputs makes no sense and it looks kind of scary (the user may only guess that the address is a change one and that it actually belongs to them).

P.S. Probably this should be addressed in a separate task after this PR is merged (though it will require a change int he protocol).
Let's maybe create an issue for this. so that it doesn't get lost (or may be we should have a single issue with the list of things to do).