App UI - layout - rework functionality

[user0]

XnViewMP 1.7.2 64bit
Windows11 (23H2), display resolution 3840x2160, win scaling 150%

General
Layout functionality spread across menus, which is inconvenient.
Also, default layout not identifiable by helmut

Suggestion

• rework Layout functionality

• add Pane (Panels) menu group
  - move app UI settings to new menu
  - group Toolbars into separate group

Example

• panes / panels

  

• workspace

  

Related

• issues
  Viewer - fix unnecessary window manipulations

• suggestions
  App UI - tools - file list - unify behavior
  App UI - layout - rework functionality (current post)
  App UI - tab - rework Dirty indicator
  App UI - tab - add drag-and-drop functionality
  App UI - tab - merge with Titlebar