dbft: move payloads/block/tx/crypto interfaces to dbft package

[AnnaShaleva]

Two parts of dBFT structure refactoring: close #90, close #91.

TODO:

• Improve documentation.
• Move all default implementations to testing code or separate place.
• Update changelog.

[codecov]

Codecov Report

Attention: Patch coverage is 66.82028% with 72 lines in your changes are missing coverage. Please review.

Project coverage is 72.30%. Comparing base (e4fad43) to head (2f4e90f).

Files	Patch %	Lines
internal/payload/consensus_message.go	66.66%	17 Missing and 2 partials ⚠️
consensus_message_type.go	0.00%	16 Missing ⚠️
config.go	72.50%	11 Missing ⚠️
internal/payload/recovery_message.go	35.29%	11 Missing ⚠️
dbft.go	82.14%	2 Missing and 3 partials ⚠️
internal/payload/change_view.go	0.00%	3 Missing ⚠️
internal/payload/constructors.go	57.14%	3 Missing ⚠️
send.go	87.50%	1 Missing and 1 partial ⚠️
check.go	50.00%	1 Missing ⚠️
internal/block/block.go	80.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #97      +/-   ##
==========================================
- Coverage   73.22%   72.30%   -0.93%     
==========================================
  Files          24       25       +1     
  Lines        1393     1390       -3     
==========================================
- Hits         1020     1005      -15     
- Misses        305      318      +13     
+ Partials       68       67       -1     

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[AnnaShaleva]

@roman-khimov, I need some initial assessment of the resulting packages structure from your side. If the direction is OK, then I'll update the documentation. The resulting built binary is smaller than the one got from master:

-rw-rw-r--  1 anna anna 189040 мар  1 22:12 build.branch
-rw-rw-r--  1 anna anna 622930 мар  1 22:11 build.master

I'm not sure how to deal with internal package. Currently dbft package doesn't depend on internal in any way, is it enough? I'm not sure if internal is excluded from build in this case.

[roman-khimov]

It looks OK except for some new exports. I'd then want to simplify payload interfaces (getters/setters suck), but that can wait.

[AnnaShaleva]

I'd then want to simplify payload interfaces (getters/setters suck), but that can wait.

We may do this in #84.