RigidBot R1 Glass Holder V2

This upgrade allows to keep stable a glass bed over the aluminium original RigidBot bed.
Having a glass removable bed simplify the process of detach objects, and avoid the bending of Y axes trying to detach objects. Just remove the glass, remove the objects over a table, and reinstall the glass. I installed a 250x250mm borosilicate glass 3 mm height.
The way RigidBot is designed makes tricky to install a glass, because the head will move over the complete surface of the bed, and also outside,