[brd] Clean up zone pour interaction

[abetusk]

Zone pours are a mess in terms of user interface. Clean them up.

Right now:

• select net
• hit 'z'
• keep hitting 'z' until you find the net highlighted that you want
• place other end of zone
• select lower right hand corner of zone
• hit 'z' again to pour

Counter intuitive and clunky. Figure out a way to make this interaction better. At the least the pour might want to happen after every move or placement.

estimate: 3
priority: high

[abetusk]

dup of #30