Preferences Subsystem Overhaul for pcb

pcb presently uses several different systems for managing user preferences across instantiations. This work proposes to unify them into a single flexible preferences subsystem that is generally extendable for use by other areas of the codebase and plug-ins.

Crosshair Rework for pcb

The crosshair is the pair of orthogonal lines used to indicate the coordinates of the next action. It serves a number of purposes related to this primary function, e.g. the position of the crosshair is restricted to grid points, snapping to objects (pins, pads, ends of lines, etc.), and objects can be attached to it...