refactor: add more types and interfaces

[faustbrian]

Proposed changes

Add types, interfaces and fix various minor issues.

Types of changes

• Refactoring (improve a current implementation without adding a new feature or fixing a bug)

Checklist

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

[codecov-io]

Codecov Report

Merging #2427 into 2.4 will decrease coverage by 0.16%.
The diff coverage is 46.26%.

@@            Coverage Diff             @@
##              2.4    #2427      +/-   ##
==========================================
- Coverage   68.08%   67.91%   -0.17%     
==========================================
  Files         385      385              
  Lines        8444     8438       -6     
  Branches      430      390      -40     
==========================================
- Hits         5749     5731      -18     
- Misses       2647     2660      +13     
+ Partials       48       47       -1

Impacted Files	Coverage Δ
packages/crypto/src/blocks/block.ts	86.66% <ø> (-0.25%)	⬇️
packages/core-utils/src/delegate-calculator.ts	100% <ø> (ø)	⬆️
...se/src/repositories/wallets-business-repository.ts	88.23% <ø> (ø)	⬆️
packages/core-utils/src/supply-calculator.ts	100% <ø> (ø)	⬆️
packages/core-container/src/config/file-loader.ts	15.62% <ø> (ø)	⬆️
packages/core-p2p/src/peer-guard.ts	82.5% <ø> (+2.01%)	⬆️
...pto/src/transactions/builders/transactions/ipfs.ts	72% <ø> (ø)	⬆️
packages/core-database/src/database-service.ts	27.48% <ø> (ø)	⬆️
.../src/repositories/delegates-business-repository.ts	84.21% <ø> (ø)	⬆️
packages/core-p2p/src/peer-communicator.ts	75.94% <ø> (-0.31%)	⬇️
... and 19 more

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[ghost]

The ci/circleci: test-node11-unit job is failing as of 6f885577246ae5330ffc1cdbe45aab816f728f5d. Please review the logs for more information.

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