QtFRED Briefing Dialog (#7032)

* initial cleanup

* rough in more code by copying from debrief

* make buildable

* prep the briefing data model

* completed data model

* activate the ui

* unused param

* stub this

* cmake list is important

* set max cam transition higher

* static cast

Author: MjnMixael

qtfred/source_groups.cmake

@@ -44,6 +44,8 @@ add_file_folder("Source/Mission/Dialogs"
 	src/mission/dialogs/AsteroidEditorDialogModel.h
 	src/mission/dialogs/BackgroundEditorDialogModel.h
 	src/mission/dialogs/BackgroundEditorDialogModel.cpp
+	src/mission/dialogs/BriefingEditorDialogModel.cpp
+    src/mission/dialogs/BriefingEditorDialogModel.h
 	src/mission/dialogs/CampaignEditorDialogModel.cpp
 	src/mission/dialogs/CampaignEditorDialogModel.h
 	src/mission/dialogs/CommandBriefingDialogModel.cpp