nicer openscad geometries for bearings
fixed typos in BOLTS FreeCAD Gui
removed BOLTS from collection names

is somehow redundant
fuse all parts of the part

this way, only a single object is contained in the exported step file.
However, it does not always work, because not all geometries are
connected. E.g. some bearings fail
work around missing uic module
harmonized backend write_output signature

and reactivated release subcommand for util script
Merge commit 'f32b542613bde3fd0'
development snapshot

should work around problems with old Qt version.