Preserved chosen GameViewPanel across sessions, added PanelMaximizer as a DockSpace manager

[xZekro51]

This PR covers two parts (which should have been split in hindsight):

• It ensures that the GameViewPanel's picked resolution is properly saved and restored on the next project session, instead of going back to Free each time
• It adds the PanelMaximizer, which acts as a DockSpace manager. The idea is that it preserves the functionality of the DockSpace from Origami, but it expands it to support panel maximizing and restoring. The maximization state is volatile and does not get saved to disk, so reloading the project after closing one with a maximized state will open with the old layout.