enhancement in Cvpcb: fast selection of components or footprint by typing the first letter of reference or footprint name

This is the first in a series of updates to the schematic library component
object code.  The goal is to eliminate the external manipulation of these
objects and push this code back into the objects themselves.  Also replace
the priority queue and internal linked list implementations with DLIST or
Boost pointer containers.

fixed: incorrect sub path calculation for libs and doc filenames (full filenames where always converted to relative paths,
even when they are not in standard libraries paths)

Small change in print function: print footprint after zones (like in BOARD::Draw) to make pads holes visible on copper zones

pcbnew: remove old of two To_User_Unit(), redraw ratsnest on/off, magnetic cursor to start move/drag module

pcbnew: Starting work on undo/redo in pcbnew. Only some delete item commands are stored in undo/redo stack

pcbnew: Starting work on undo/redo in pcbnew. Only some delete item commands are stored in undo/redo stack