Many more schematics changes

[IJeffray]

A bumper stack of 9 commits comprising the past 2 days work - lots of small detail changes, including:

• Support for global references in labels (no more '=Project' etc appearing)
• Very crude support for beziers - just as a polyline
• Embryonic support for pin symbols - for now, just the "not" symbol on a pin, which was critical for me.
• Mild improvement to the elliptical arc support
• Add support for overbars so altiu, backslash notation is converted to kicad grouped tilde notation
• Change reference matching to be case insensitive, as Altium seems to be (more labels now work)
• Hide junk that Altium seems to dump off the bottom of the page
• More tweaks to port and sheet entry support, with a big caveat (see commit message on that commit)
• Improvements to comment block handling

[thesourcerer8]

Thanks a lot!