TDD - Lib files cleanup and reorganization

Opening early to discuss the changes.

## New structure

- `app/lib` contains Katello dependent libs. Classes are auto-loaded and reloaded by Rails. Classes has to be placed based on theirs namespace.
- `lib` explicitly loaded (`require 'a_lib'`) libraries. (They are not auto-loaded or reloaded by Rails)

**TL;DR:** Libraries are in `app/lib`, organized by namespace, auto-loaded and reloaded.

## TODO

- [x] reorganization
- [x] cleanup old requires
- [ ] *90%* check packaging
- [ ] *33%* util cleanup