Reduce Compilation Time by Refactoring Include Directives and/or hpp-cpp Implementation Divisions

Hey Monkeys!

**User Story**
As the `(ape) programmer` I want `(banana) fast compilation time` so that it is easier to work with the code base.

I would like to try reducing the compilation time with the two following approaches:
* refactor include directives: They are pretty messy and many files include unneeded files.
* refactor hpp/cpp implementations: Maybe some often-included headers including implementations could be factored out into cpp files providing some benefits for the compilation time.

**Impacts**
- [ ] API (the application programming interface)
- [x] Build (the build process or something prior to compiled code)
- [ ] CLI (the command line wallet)
- [ ] Deployment (the deployment process after building such as Docker, Travis, etc.)
- [ ] DEX (the Decentralized EXchange, market engine, etc.)
- [ ] P2P (the peer-to-peer network for transaction/block propagation)
- [ ] Performance (system or user efficiency, etc.)
- [ ] Protocol (the blockchain logic, consensus, validation, etc.)
- [ ] Security (the security of system or user data, etc.)
- [ ] UX (the User Experience)
- [ ] Other (please add below)

## CORE TEAM TASK LIST
- [x] Evaluate / Prioritize Feature Request
- [ ] Refine User Stories / Requirements
- [ ] Define Test Cases
- [ ] Design / Develop Solution
- [ ] Perform QA/Testing
- [ ] Update Documentation

Ape out!

No files, tests, or entry points are named. Start by measuring the current compilation time and inspecting the project's include directives and hpp/cpp implementation divisions. Done means a documented refactoring reduces compilation time without breaking the build.

Written by the indexing model from the issue text.