Replace DIM() macro

The standard DIM() macro was not typesafe as it happily deferred errors
to runtime that can be caught at compile time.  Replacing it with a
generic C++11 constexpr allows for typecasting, comparison and compile
time error checking.

pcbnew/plot_board_layers.cpp

@@ -672,7 +672,7 @@ void PlotLayerOutlines( BOARD* aBoard, PLOTTER* aPlotter,
 
     SHAPE_POLY_SET outlines;
 
-    for( LSEQ seq = aLayerMask.Seq( plot_seq, DIM( plot_seq ) );  seq;  ++seq )
+    for( LSEQ seq = aLayerMask.Seq( plot_seq, arrayDim( plot_seq ) );  seq;  ++seq )
     {
         PCB_LAYER_ID layer = *seq;