Check command name/path for truncation and provide user feedback during
config parse (and use conf_cmd_add to populate defaults); based on a
discussion with Tiago Cunha.  While this looks ugly, there are likely
some other changes here to come.
Much like we do for keyboard and mouse bindings, remove duplicates for
command name - last match.
Merge keybinding and mousebinding queues into using the same merged
struct, binding; they were essentially the same accept for what was
'pressed', keysym or button.
keybinding -> key binding
Minimize trivial differences between a few kb and mb functions.