schemas/VegCore/VegCore.ERD.mwb: plot: replaced bounding_box_rect with length_m, width_m, since the bounding box was intended to store plot dimensions (along the plot azimuth) rather than an actual bounding box aligned to the compass directions. added azimuth_deg_N, which is used to resolve plot element x/y coordinates to absolute geocoordinates while taking into account the rotation of the plot.