[Meta] Code clean up on D8 branch

Problem/Motivation

Quora have just been ported to D8 and in dev state. After reviewing the code, I found that we need to clean up code on 8.x branch to be more closer to Drupal 8. Readme.txt leads no where how to create API IDs and CX.

Proposed resolution

1. Use Dependency Injection.
2. Move data manipulation functions as Services
3. Use calss FromBase for building forms.
4. Clean quora.module file.
5. Proper explanations in Read me file.
6. Add link configuration settings in UI.

File different issues for each file and add as child issues.

Remaining tasks

1. use Dependency Injection in classes instead of \Drupal.
2. Adjust String translation functions.
3. Use CMI best practices.
4. Use actual fields instead of psuedo fields from content type to be displayed as options on configuration settings.
5. Move helper functions as services methods.
6. Better field descriptions.
7. Update READEME.txt.
8. Correct config key in info.yml.
9. Add parent in links.menu.yml.