[Fix and Re-enable ] AppModel Area - Feature Test

**The following tests were disabled while open-sourcing the test area:**
Common dialogs [ /Subarea=Commondialog ]
- [ ] CommonDialog_OpenCustomPlace
- [x] CommonDialog_CustomPlaceCases
- [x] CommonDialog_FileDialogCustomPlaceCases
- [x] CommonDialog_OpenFileIsThreadModal
- [x] CommonDialog_OpenFileBeforeShow
- [x] CommonDialog_SaveFileIsThreadModal
- [x] CommonDialog_OpenFileOnSecondThread
- [x] CommonDialog_SaveFileOnSecondThread

Navigation:
- [ ] NavigateUri
- [ ] FragmentNavigationStandalone
- [ ] SandboxExternalContentStandalone
- [ ] NavigationFailedStandalone
- [ ] CredentialPolicyPreserved

Journal
- [ ] NavigateToNull1
- [ ] NavigateToNull2
- [ ] NavigateToNull3
- [ ] NavigateToNull4
- [ ] NavigateToNull5
- [ ] NavigateToNull6
- [ ] AddBackEntryOnEmptyNSXBap
- [ ] JournalEachChangeXbap
- [ ] ReloadCurrentPageXBap
- [ ] GoBackXbap
- [ ] CustomJournalingGoForwardXbap
- [ ] RemoveBackEntryAndGoBackXbap
- [ ] NavigateAwayAndReturnXbap
- [ ] StopNavigationAndReloadXbap
- [ ] NavigateToFragmentXbap

The cause of failure is not known as of now. It may be that the tests themselves need to be fixed.

**For re-enabling the tests -**
1. Search for the methods named as above in the code.
2. Comment out the DisabledTestCase attribute before the test function.

**To run the tests in isolation, use the following command:**
```
.\RunTests.cmd /Area=AppModel /Name=
```
is the full name mentioned above in the list

**To run a subarea:**
```
.\RunTests.cmd /Area=AppModel /Subarea=
```
is the full name of the Subarea (like: Journal, commondialog)

For debugging the tests, add the /DebugTests argument in the command above.

Related issue: [Microsuite] Failures AppModel & Editing #49