Reduce code duplication in `bug reporting`, `team response` and `tester response` views

As [suggested](https://github.com/CATcher-org/CATcher/pull/984#pullrequestreview-1134105253) by @gycgabriel, we can reduce the duplication in the code that checks if a user has made any changes to the issue or response while in edit mode.

### Context
This feature was introduced in the following PRs:
- #985
- #984

This was done to ensure that the when the user leaves edit mode, the cancel edit warning dialog box (that warns the user that some changes made will be discarded) is only shown if he/she has actually made any changes to the issue or response.

### Where the code duplication is
The method to detect changes `openCancelDialogIfModified` is currently declared in 4 separate components (shown below):

https://github.com/CATcher-org/CATcher/blob/660e01726df9c5a499c4d320cb75f8393bb486b8/src/app/shared/issue/title/title.component.ts#L83-L92

https://github.com/CATcher-org/CATcher/blob/660e01726df9c5a499c4d320cb75f8393bb486b8/src/app/shared/issue/description/description.component.ts#L121-L130

https://github.com/CATcher-org/CATcher/blob/660e01726df9c5a499c4d320cb75f8393bb486b8/src/app/shared/view-issue/team-response/team-response.component.ts#L151-L161

https://github.com/CATcher-org/CATcher/blob/660e01726df9c5a499c4d320cb75f8393bb486b8/src/app/shared/view-issue/tester-response/tester-response.component.ts#L142-L172

### What can be done
There is an opportunity to reduce code duplication, possibly by moving this function into a service.