Several fixes and changes with window layouts (workspaces):
- The wording "window layouts" has been used for historical reasons but workspace is more common.
- Turning workspace buttons into drop down button.
- Rearranged menu items in menu View/Workspaces.
- Removed "Arrange Windows" function. It's not really needed anymore since the windows snap to each other now. It was often causing confusion when it has undesired results.
- Removed embedded windows mode.
- Reduced flickering when switching workspaces.
- When holding Ctrl on window move/sizing, snapping is disabled.
- When sizing main window then windows inside the main window keep their aspect ratio.

Middle mouse button on brush container slot deletes the slot.

Fix: Now stopping animation playback when dropping a file onto the UI.

Fix: Formula paint mode was applied multiple times during stroke.

Fix: Using "Save As" with brush container and cancel showed an error.

Fix: Color editing dialog not working correctly. When using the dialog for editing a single color in non-palette mode, e.g. in the preferences for the transparency checker pattern colors, then the RGB edit fields did not work correctly.
Also, a display glitch at the color range gradients of a single channel sometimes showed pure white instead of the gradient when opening the dialog.

Fix: Intro dialog interfered with canvas window and did not close.

Fix: A layer blend mode different than "Normal" could not be reset to "Normal".

Fix: It could happen that some of the application windows use a wrong width.