fixed filename

case in base file has to be the same as case in the file system.
Otherwise things go wrong on linux.
add units to designtables
started adding set screws
Added inch sizes to base

To do that:
-Renamed keys to legal design table configuration names (and added
probable thread pitches).
-Added "e_min" column data to hexagonnut3 in nut.blt

Also turned on dual dimensions in the nut.sldprt
wrote spec for different drawing types
testcases for drawings
implementation for drawings
adapt backends
change drawing types to drawing-dimensions
connector drawings helper backend

This backend automatically generates scad files for the missing
connector drawings.
added connector drawings for all classes with connectors
ignore connectordrawings backend output
regenerated html
removed accidentially commited scad files
rewrote base widget import slightly different

Some people are experiencing problems with PySide that I cannot
reproduce. Maybe this helps, but it is a long shot.
new development snapshot
regenerated html
Changed default key to be a valid selection from new keys
Updated Nut file naming
Updated default in nut.blt