New param to decide to close the bottom of the object

[JimmyDaSilva]

As the object during capture is place on the board you are never able to see the bottom of the object. During reconstruction this leads to creating a hole in the object that does not actually exist.

Like proposed there wg-perception/capture#18 , I guess the proper way would be to flip the object and do a second capture, then use some alignment algorithm in PCL to get a fusion of the two capture and hence get a full object for reconstruction.

For now, I am worked a little on the Meshlab scripts and found a way to add a flat bottom to the object by using its convex hull. You just have to use the --close flag to add a bottom to the object.

See the difference here:

I have tested it on several objects, and it seems to work fine.
This is a fine temporary hack before we code a nice way of aligning twoo set of captures.
For example, my hack won't fix this, because there is no points below the camera lens