PSPreferencesController.[hm]: Filter hot keys. Read and write to
preferences.
NJRHotKeyField.[hm]: Added property list serialization of hot key data
(not quite like PSAlarm/Alert because we're a GUI element). Added
delegate method for hot key filtering and action triggering when hot
key set or cleared. Only use filtered modifiers to avoid bizarre
behavior. More bug fixes.
English.lproj/Preferences.nib: Connected Clear button. Connected
NJRHotKeyField delegate and target to PSPreferencesController.
NSString-NJRExtensions.[hm]: Replaced "...modifierMask" with
"...modifierFlags" because it's more appropriate.