Pcbnew: code cleaning in polygons

This is an obscure legacy code from FreePCB, never used, never tested, never maintained.

Remove arcs support in zone outlines: this is a legacy code from FreePCB, never used, never tested, never maintained.

Some coding style policy fix.

Footprint wizard converts from user units to internal units back and forth, so user can type in mm or mils now

Eeschema: fix a bug that crashes eeschema (only when compiled in debug mode) when creating a new wire, and when any wire orientation is allowed.

Pcbnew: more about keepout areas: remove keepout for pads option and add keepout for copper zones option.
Export keepout to Specctra DSN file.

This is *a work in progress*, so some features are missing, and/or could be modified.
Mainly keepout zones are not yet exported to autorouters, and pads are not taken in account.
Some code cleanup in polygon.*

Fix incorrect import of smd pads from Gpcb.
Very minor change in dialog print.

Eeschema: bug fix: when creating new connections, junctions were not always automatically added when needed.
Fix an other minor bug.

Add copy to text items in pcbnew. Automatically mirror text items added to back silkscreen (bug 1017446).