Base acrylic: USB power adapter

Increased USB power adapter top screw hole to oval to accommodate both
board versions (2 places)
Removed J from USB power spacer for Model B plus compatibility
Case: Removed vertical mount

Vertical mount is a point of failure for the acrylic (especially as
when mounted, the lid has huge leverage to snap the mount notch).  When
the screw holes are adjusted for Model B+ compatibility, this we be
even worse.  Additionally, it may have little practical use, as the
case can stand vertically.

May revisit at a later time.
Case: widened base feet

Moved feet to edges of board to make more room for side holes needed
for Model B+ compatibility.
Case: Added Blank lid

Added first cut blank lid, with rubber band straps and mounting holes.
Case: base additions

Keyed PCB header.  Added vertical elastic band straps.
Case: Refactored straps

Made better vertical rubber band straps in base.  Changed straps in
blank lid.  Adjusted mounting holes.
Adjust lid retention clip.  New sidewall.

New sidewall has slightly wider fated clip heads to reduce chance of
over bending.  To be tested.