The executable name constants are only used by two files, they do not
have to be in common.h.
Also converted to const wxString for better type-safety and removed
old-style wxT macros.
For a start, this contains the GAL display settings (AA settings and
grid styling).
In future, other modedit-specific settings could go here too.
Fixes: lp:1672150
* https://bugs.launchpad.net/kicad/+bug/1672150
SELECTION now holds EDA_ITEMs not BOARD_ITEMs so various places had to
change to casting the selected items to BOARD_ITEMs.
Fixed compilation warnings on clang (Tom)
When creating a copy of CONTEXT_MENU, always a CONTEXT_MENU instance was
constructed, whereas an inherited type should be used. Solved with
CONTEXT_MENU::create() that has to be overridden in inheriting classes.
Event & update handlers are now virtual functions, instead of setting
the handlers with Set{Event,Update}Handler().