Editor UI/UX: Floating window mode

[Jowan-Spooner]

Initial implementation of a "floating" mode for the dialogic editor.

Known problems:

• when in floating mode, pressing the Dialogic tab will focus the window. However it also show the main editor screen, which is just empty. Ideally this would do the same as the script tab when the script editor is floating, but it might be impossible.
• when closing the floating window while another tab is open, both editors can be open at once (embedded)
• floating window doesn't care for the minimum size of the controls which can lead to UI breaking.
• dialogic doesn't remember floating state nor position. We should save both in _get_window_layout() and set them with _set_window_layout()

Would fix #1878