Move bitmaps.h out of base_struct.h

bitmaps.h was included in nearly every file in the project due to it
being included by base_struct.h

Only about 130 files actually use the XPM definitions defined there, and
many of those already included bitmaps.h themselves, or via
menu_helpers.h. However, touching bitmaps.h would result in over 400
rebuilt files for pcbnew alone.

This commit moves the bitmap-related types like BITMAT_DEF out to a new
header, which is still included by base_struct.h, which is less
avoidable for now, it's it's used in the interface.

The icon list is still in bitmaps.h. This has the side effect that's
it's now easier to automatically generate this file.

Many classes in pcbnew and eeschema needed some functions moved
to the implementaitons from the headers too.

eeschema/sch_bitmap.cpp

@@ -30,6 +30,8 @@
 #include <class_drawpanel.h>
 #include <trigo.h>
 #include <macros.h>
+#include <bitmaps.h>
+
 #include <sch_bitmap.h>
 
 #include <wx/mstream.h>
@@ -309,3 +311,9 @@ void SCH_BITMAP::Plot( PLOTTER* aPlotter )
 {
     m_image->PlotImage( aPlotter, m_pos, GetLayerColor( GetLayer() ), GetPenSize() );
 }
+
+
+BITMAP_DEF SCH_BITMAP::GetMenuImage() const
+{
+    return image_xpm;
+}