fix issue with empty frame with generated ST code

fix not saving location address from variable panel

this regression was introduced by commit 3518d10

add $(Beremiz installation)/mingw/bin in PATH on Windows platform

This fixes issue if multiple gcc installation are found in user's
PATH. Now gcc from Beremiz is used by default.

fix issue with non-working global hotkeys in IEC code panel

add more comments to svgui example

cleanup traffic lights example

cleanup svgui example

Fix bug with two or more wires connected to one input. Now only one wire can be connected to one input, except BOOLean signals in LD and SFC. If user trying to connect wire with already connected input, wire highlight will become red.
Signed-off-by: Andrey Skvortsov <andrej.skvortzov@gmail.com>