Also fixes a bug where nets wouldn't get changed because the
pads weren't changed and so the pad nets would propagate and
wipe out the changed nets on the tracks.
Also includes warning dialogs that pad nets will be changed if the
track nets are.
Fixes: lp:1779854
* https://bugs.launchpad.net/kicad/+bug/1779854
- renamed connectivity.[h|cpp] to connectivity_data [.h|.cpp] so that the file name matches the main class name.
- GetNetItems() now returns a vector instead of a list