Turtle Art: Keep block palette in fixed location, not scrolling with workspace

[Mokurai]

When composing Turtle Art stacks too long for the screen, it is currently necessary to scroll up and down constantly to get blocks, and then move them by stages down to where they are needed. The same is true for putting unneeded blocks in the trash when taking them out of stacks. Removing the palettes from the workspace, and keeping them in place just below the toolbar, would remove this necessity and speed up programming.

Discussed with Walter Bender, who approves.

[walter]

This will take a bit of work: the approach I think I will take is to make the palette be a separate window from the scrolled window. But then I need to check for mouse events in each window and maintain multiple sprite libraries, as they are associated with a window (probably something else I should fix). Stay tuned.

[walter]

In v117, the palette floats with the scrolling window.

See ​http://git.sugarlabs.org/turtleart/mainline/commit/cfe83381911269f6863b4703e635bed6a23a9c31

[walter]

Fixed in v117