refactor: add types, remove dead code and unused imports

[faustbrian]

Proposed changes

• Add more type hints
• Add more return types
• Add more interfaces
• Remove dead code
• Remove unused imports
• Reduce complexity of a few classes
• Ensure satoshi values are stored as strings in files

Types of changes

• Refactoring (improve a current implementation without adding a new feature or fixing a bug)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist

• I have read the CONTRIBUTING documentation
• Lint and unit tests pass locally with my changes

[ghost]

The ci/circleci: test-node10-integration-0 job is failing as of a2e37bbacd41332109cb38ee30346f23b253523b. Please review the logs for more information.

Once you've pushed the fixes, the build will automatically re-run. Thanks!

[codecov-io]

Codecov Report

Merging #2420 into 2.4 will decrease coverage by 1.86%.
The diff coverage is 80.88%.

@@            Coverage Diff             @@
##              2.4    #2420      +/-   ##
==========================================
- Coverage   68.17%   66.31%   -1.87%     
==========================================
  Files         400      398       -2     
  Lines        8592     8565      -27     
  Branches      433      432       -1     
==========================================
- Hits         5858     5680     -178     
- Misses       2686     2838     +152     
+ Partials       48       47       -1

Impacted Files	Coverage Δ
...kages/core-api/src/versions/2/peers/transformer.ts	66.66% <ø> (-13.34%)	⬇️
packages/core/src/commands/snapshot/rollback.ts	0% <ø> (ø)	⬆️
packages/core-api/src/versions/1/utils.ts	92.3% <ø> (ø)	⬆️
packages/core-transaction-pool/src/utils.ts	0% <ø> (ø)	⬆️
packages/crypto/src/crypto/crypto.ts	90.69% <ø> (ø)	⬆️
packages/core/src/commands/config/publish.ts	0% <ø> (ø)	⬆️
packages/core-api/src/versions/2/rounds/schema.ts	100% <ø> (ø)	⬆️
...ackages/core-transactions/src/handlers/transfer.ts	66.66% <ø> (ø)	⬆️
...kages/core-api/src/versions/1/peers/transformer.ts	100% <ø> (ø)	⬆️
...kages/core-api/src/versions/2/delegates/methods.ts	89.65% <ø> (ø)	⬆️
... and 48 more

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