Add original wheel 1.0 DXF and improved wheel 1.1 CamBam files.

hi Andrew, here are the SimpleBot wheel assets.  You'll notice that the original 1.0 version is DXF, then I made the small improvement (centre hole) using CamBam.  So, there is inconsistency in the asset formats.

In time, it would be best to get all the original master assets in InkScape (as per the bases and bumpers) as effectively the "source code" all in one directory.  And, perhaps have another directory which contains processed files, e.g CamBam and GCode, so that we can easily produce more physical copies (just like existing ones) directly on the laser cutter, without having to perform the processing again.