* [Companion] Refactor MdiChild & TreeModel, restore drag/drop, and more:
* Add full drag-and-drop functions to the models list, including model copy, move, and insert actions (also between windows);
* Add general radio settings copy/paste across file windows;
* Full MIME support with distinct types for various data (eg. models vs. general settings), also add new type for metadata (header);
* Copied/cut models can now be inserted in any spot (similar to drop-insert);
* Deleted/cut models can now be removed entirely (including the empty slot) for all radio types (any models after the removed one move up, like for Horus) (may need to make this an option);
* Empty model slots can now also be removed (any models after the removed slot move up) (but total # of slots is still maintained);
* Default model can be deleted (new default is picked);
* Completely revamp the actions system (copy/paste/edit/etc) to make it fully functional:
* Actions exist in the window, not just context menu, therefore all keyboard shortcuts actually work, w/out any duplicated code;
* Provides access from MainWindow in a comprehensive manner: all actions are available and properly updated based on selections in current editor window, w/out awkward event monitoring;
* More actions available from context menu, and somewhat reorganized;
* Also show all actions on mini toolbars right in the MDI window (possibly make optional later);
* Updated English localization file to account for plurals usage in new action item names (other languages need to be updated);
* Keyboard navigation in the model list now works/practical;
* MDI window uses all available height by default;
* Newly added models/categories are selected and highlighted; Category names are immediately editable; Model editor is/can be launched if wizard is not (need to make option);
* MainWindow updates:
* Edit toolbar and menu now showing all available edit actions, with proper context;
* File menu properly updates with all "general" radio actions: edit/copy/paste settings and simulate radio;
* Added Windows menu showing list of open windows (eg. to switch when full screen) and tabbed window option (need to make persistent setting);
* Immediate update of icon size preference;
* Do not delete toolbars when re-translating UI (they don't lose assigned position);
* [Companion] Restore model compare functionality by using new MIME data exchange system; Add ability to compare any number of models at a time; Multi-model printer now shows custom hardware settings for each dropped model (even from different radios).
* [Companion] Add missing monoblue & monowhite theme sdsync icons.
* [Companion] Model wizard starts with default model name populated.
* [Companion] Properly re-translate UI instead of recreating all the actions/etc.; Tell Mac specifically where to put our actions (seems to make it happier too).
* [Companion] Further improve handling of Window menu items/detection of sub-window changes.
* [Companion] Add file-close action.
* [Companion] Add user options and save preferences:
* Option to use wizard, open editor, or do nothing on new model creation;
* Option to remove empty model slots when deleting/moving models (in non-Horus radios);
* Options to hide toolbars in document windows (r-click on TBs);
* Save/restore size of document windows, and maximized/tabbed state;
* Save/restore size/position of model compare window;
* Add shortcuts for model compare, FW download, log viewer;
* [Companion] Disable being able to "delete" empty model slots (more awkward than helpful).
* [Companion] MdiChild now use a QTreeWidget instead of a QListWidget (for Horus compatibility)
* [Companion] Horus models.txt parsing / writing implemented
* Fix for QT53 (#4109)
