Refactor IssueTablesComponent

[yucongkoo]

While implementing the new UI for bug reporting phase in #1312, I noticed some places that I could be further improved in terms of code quality, mainly the following 2 aspects:

• Duplication of code between deleteIssue and undeleteIssue, they are essentially performing the same actions, but in reverse directions, hence the code is highly duplicated.
• There are 2 separate lists issuesPendingDeletion and issuesPendingRestore, which is used for displaying the loading icon (instead of the delete/restore icon), we can actually merge these 2 lists into a single list (maybe issuesPendingAction?) instead and display the loading icon (and hide the delete/restore icon) based on this list
• There is a lot of conditional logic in the issue-tables.component.html file, we should probably move these logic into the issue-tables.component.ts file instead. See the *ngIf=...

[Arif-Khalid]

This is a good enhancement which I agree with. Labels assigned are appropriate.
If the component isn't inherently refactored by #1309 , I would recommend setting this issue as a good-first-issue for new contributors and leaving it for them.