Don't hardcode modifier masks in the wheel and keyboard input
controllers. Instead, hardcode accelerator strings and get the right
modifier mask from gtk_accelerator_parse() at runtime.
This turns e.g. "<Shift><Primary>" into Shift+Cmd on OS X and into
Shift+Ctrl on X11 and Windows.
Also rename the events accordingly and change the event names in the
default controllerrc.
Unrelated: reorder the actions so the ones with less modifiers are
listed first, and change the order of action matching to match the
actions with most modifiers (the last ones) first.
e50103ccda