Improved lenscap - parametric

Based on leemorton123's parametric lens cap but heavily reworked to avoid bridging and overhangs, to give a very functional lens cap. STL files are generated with diameter=76mm in order to fit a 77mm lens.

Prints in 4 parts and clips together.

Updated to address some issues with hole placement on smaller caps, and to try to support the online customiser.

I had some issues getting the online customiser to work - though I hope they are resolved. If you can't get it to work in customiser, try downloading the SCAD file and making the changes using OpenScad - but also be aware that for smaller lens caps you may need to adjust the number and/or size of the studs.