PROPERTIES object has been recreated every time it was needed, using
two fields in PART_LIB class. Now the buffering & caching settings are
stored directly in a PROPERTIES object.
* Factor out PROPERTIES object from the PCB plugin code and move it into
common so it can be used by both the Pcbnew and Eeschema plugins.
* Add schematic I/O plugin manager for loading and saving schematic and
component library files.
* Add initial attempt at a parser for current schematic file format. This
parser will be infinitely more strict than the current parser which is very
forgiving in what it parses.
* Make minor changes to the base bitmap class to support the new parser.
* Add find root sheet support to sheet object to allow fetching the root
sheet from any sheet in the stack.
Seth Hillbrand
Maciej Suminski
Wayne Stambaugh