Remove unused code from CATcher

[chunweii]

Since WATcher is a fork from CATcher, there are still many instances of old and unused code from CATcher. Let's remove these codes.

• DataService (used to access data.csv in CATcher)
• src/app/core/services/session-fix-confirmation (component to ask user for permission to create a new repository)
• fetchSettingsFile() and fetchDataFile() in github.service.ts
• Creating and updating issues in issue.service.ts
• All tests related to the above

There could be more unused code in the project. These are some that I have found

• [x] - Remove unused services in src/app/core/services
• [x] - Remove unused component from src/app/core/services/session-fix-confirmation
• [x] - Remove unused models in src/app/core/models

[vigneshsankariyer1234567890]

Adding some more after my personal investigation

• All files in src/app/core/models/conflict
• All files in src/app/core/models/generators
• Seems like a lot of models in src/app/core/models/github are used by unused methods in issue.service.ts
• and many more...

Perhaps we can break up the task into sub-tasks by folders? That way the tasks are much more easier to complete, rather than having to go through all the folders within one issue. Wdyt @chunweii ?

[chunweii]

Yes, we should break fix this issue in several PRs. Removing all unused code in 1 PR might be too big of a change.

[chia-yh]

I noticed profileForm in session-selection.component.ts doesn't appear to be used currently, are there any plans on utilising Profiles in WATcher in the future? There are also some methods associated with it (e.g. initProfileForm, onProfileSelect) that could be candidates for removal in the case that there are no future plans for using Profile with WATcher.