Match IJ1 drawing tool conventions

Wayne Rasband reported in the ImageJ mailing list:

> In the ImageJ 1.47 daily build, thanks to Michael Schmid, the built in (selected from the toolbar's ">>" menu) Brush, Overlay Brush and Pencil tools work this way:
> - Shift-drag constrains drawing to be horizontal or vertical
> - Shift-ctrl-drag changes the cursor size
> - Ctrl selects the foreground color
> - Alt-drag draws in the background color
>
> On Macs, use the command key instead of the control key.

We should support these conventions if possible.

Migrated-From: http://trac.imagej.net/ticket/1352

The issue names no files or tests. Start by locating the Brush, Overlay Brush, and Pencil tool implementations and their mouse and key event handling; verify the listed Shift/Ctrl/Alt conventions, including Command on macOS, with the project's available tests or manual checks.

Written by the indexing model from the issue text.