Component interfaces scattered and scarcely documented

[matejpavlovic]

Define the interfaces of the following components in a clean and structured way, and write readmes.

• Request store
• Write-ahead log
• State machine
• Networking
• Application
• Client request dissemination

[matejpavlovic]

All module interfaces are now gathered in the /pkg/modules package and most of them are documented using comments.
Modules have been added, removed, and renamed.
Some parts of the documentation are still missing, but separate issues will be opened for addressing those.