[sch/brd] contextual menu

[abetusk]

As a start, provide a context menu popup to change values or to do other actions. Double right click should bring it up.

Some basic actions that can be put in:

• change font size
• change icon sizes
• sliding clearance
• sliding trace width
• layer hiding

The above don't need to be implemented, this ticket is about creating the contextual menu interface so that actions can be embedded in them.

priority: medium estimate: 2

[abetusk]

Add a tool that brings up a list of options to change. For each option have sliders?

[abetusk]

Can also put in zone information into it to help ease the pain of creating pours.