* 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.
Currently, kicad_pcb files have a (version ...) tag, but it is ignored. This
commit does the following:
1. Parse the version. If it's later than the last supported version, present an
alternative error message suggesting an upgrade if the file does not load
correctly. The version will be interpreted as an integer YYYYMMDD to suggest
a KiCad release date.
2. Accept a (version ...) tag also in kicad_mod files, but do not write them
yet. If no version tag is present in these files, assume the version to be that
of the current format version at the time of this commit.
This is meant to be merged to the 4.x stable series, and preps for KiCad 5
which will start emitting version tags also in footprints - users with what
will then be 'old stable' will not get a parse error when we introduce this for
footprints, and we can safely increment the format version later.
*) Move button handlers to LEFT MOUSE CLICK from COMMAND events, so wxGrid focus is not lost.
*) Sketch out the concept of COW support for the GITHUB_PLUGIN in its @todo.