New feature: be able to set filtered caps on links.

New feature: be able to fixate caps on links.

Right-clicking on a pad gives a menu that includes "Pad status...",
which does nothing.

The pad tab in the element property window contains only the pad
template caps, in a poor format.  It would be nice to have pad
template caps, getcaps(), and currently set caps.

Bonus feature: change the color of links that are unconstrained
(basically, the getcaps intersection is not fixed, so the link
caps required fixation.)

When "sort" is enabled, clicking and dragging elements should
tie their position to the cursor, not floating w.r.t. the cursor.

new feature: Add element by typing name.

Dump debugging information to a window instead of the terminal.

Make "sort" smarter.