QtFRED Variables Dialog (#7020)

* refactor variables/containers model and variables ui

* get containers working

* switch to tab view and add filters

* fix the filters

* fixes

* ooo

* static casts

* more static cast

* unused

* clang

Author: MjnMixael

qtfred/source_groups.cmake

@@ -248,6 +248,8 @@ add_file_folder("Source/UI/Util"
 add_file_folder("Source/UI/Widgets"
     src/ui/widgets/ColorComboBox.cpp
     src/ui/widgets/ColorComboBox.h
+	src/ui/widgets/LineEditDelegate.cpp
+	src/ui/widgets/LineEditDelegate.h
 	src/ui/widgets/FlagList.cpp
 	src/ui/widgets/FlagList.h
 	src/ui/widgets/NoWheelComboBox.cpp