Don't allow configuration of two mutually exclusive operating modes

[mirvin]

Problem:
Bugzilla ServiceHostConfigTool.exe allows a user to enter data in to both tagged and assigned modes. This causes confusion for the user. This is ultra troublesome when coupled with this error that hides one of the configurations #2

Reproduce:

1. Start the ServiceHostConfigTool.exe
2. Enter VersionOne configuration
3. Click on the Services->Bugzilla tab
4. Select "Tag defects by field values and populate fields in the "Tag" section.
5. Select "Assign defects to user" and populate fields in the "Assign" section.
6. Click the X to close the window and save accordingly. Warning! Confirm that you are saving in the correct path in your dialog box!
7. Execute the ServiceHostConfigTool.exe
8. Go to the Services->Bugzilla tab
9. Select "Tag defects by field values" and observe that the content is saved in the "Tag defects by field values" configuration area.
10. Select "Assign defects to user" and observe that the content is saved in the "Assign defects to user" configuration area.