add proposer::TransactionPicker

[scravy]

This adds a class named TransactionPicker and introduces a new namespace proposer in its own directory. I sort of got fed up of the untestability of bitcoin and that everything is intertwined with each other directly.

In order to propose a block I need to build one which is I have to (1) pick transactions (2) put a coinstake transaction (includes block height, signature, reward output) (3) sign the thing. Picking transactions is already implemented in bitcoin but it's well buried inside CBlockAssembler which does too many things at once for my taste + deals with that horrendous CBlockTemplate (see comment in BlockAssemblerAdapter in the source).

Since I want my Proposer to be testable and (1+2+3) are essentially simple operations I want the code to be simple. So here is the part which performs 1, by delegating to bitcoin's block assembler (for now). This way I do not have to change the block assembler or overwrite the coinbase transaction in the block template.

I would be interested in hearing your thoughts about my approach, as I intend to follow it with everything I do from now on. Maybe you are fundamentally opposed to virtual methods or whatever.

In bitcoin there have been small efforts to extract things into Interfaces (CValidationInterface for instance) also. More recent work is on separating wallet and node and also here they start to create interfaces (bitcoin/bitcoin#14437, src/interfaces).

[Gnappuraz]

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[scravy]

@Gnappuraz Thanks for your approval :-)

@AM5800 @Ruteri WDYT? I'd be very much interested in your opinion.

[kostyantyn]

my personal opinion: avoid any collisions, e.g., all these names should be unique:

1. namespace
2. class name
3. function names
4. local variables

Otherwise, it can confuse the reader. maybe think of another name for it?
and then you don't need to explicitly use class keyword when instantiating the object.
new class BlockAssemblerAdapter(chainParams));

[kostyantyn]

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[cornelius]

I like the concept. Just some small questions about conventions in the other comments.

[AM5800]

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[scravy]

For the newcommers: When reviewing we try to stick to the contribution guidelines outlined by bitcoin, which are documented in https://github.com/dtr-org/unit-e/blob/master/CONTRIBUTING.md#peer-review

Additionally we use githubs review/approve mechanism.

[frolosofsky]

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[nzmdn]

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