New --init-docks command-line option completes Qt docks

[Edward K. Ream]

I spent most of yesterday polishing how Leo handles Qt docks.  Most of the work involved #1193, which fixed the viewrendered.py plugin so it creates a Render dock.

All this work creates the illusion of simplicity where in fact none exists ;-)  That was inevitable, considering that docks should "just work" regardless of:

- The -no-dock command-line option.

- The @bool use-vr-dock user setting.

- Where the user drags various docks.

The final piece of the puzzle is the new --init-docks command line arg.  This puts docks in standard places, without you having to clear Leo's caches! See #1205 for more details.  Use this if docks get stuck in unwanted positions.

Note that --init-docks puts the Render dock appears alongside the body pane.  This is necessary, because at present there is no way to do so by dragging.  If (and only if!) @bool use-vr-dock is True you may then move the Render dock where you like.

Summary

The viewrendered plugin creates a Render dock (unless --no-dock is True).

@bool use-vr-dock = False puts the Render dock in its legacy position.

Use the --init-docks command-line arg if docks get stuck in unwanted positions.  You don't have to clear caches anymore.

Edward