Add Provision to Force Use of DeviceType.UNKNOWN Devices

[ewhac]

I'm working on a driver for the old Logitech G13 gaming keypad. Here's the current capability mapping (subject to minor change):

{
    ('EV_SYN', 0): [('SYN_REPORT', 0), ('SYN_CONFIG', 1)],
    ('EV_KEY', 1): [
        ('KEY_LIGHTS_TOGGLE', 542),
        ('KEY_MACRO1', 656), ('KEY_MACRO2', 657), ('KEY_MACRO3', 658), ('KEY_MACRO4', 659),
        ('KEY_MACRO5', 660), ('KEY_MACRO6', 661), ('KEY_MACRO7', 662), ('KEY_MACRO8', 663),
        ('KEY_MACRO9', 664), ('KEY_MACRO10', 665), ('KEY_MACRO11', 666), ('KEY_MACRO12', 667),
        ('KEY_MACRO13', 668), ('KEY_MACRO14', 669), ('KEY_MACRO15', 670), ('KEY_MACRO16', 671),
        ('KEY_MACRO17', 672), ('KEY_MACRO18', 673), ('KEY_MACRO19', 674), ('KEY_MACRO20', 675),
        ('KEY_MACRO21', 676), ('KEY_MACRO22', 677),
        ('KEY_MACRO_RECORD_START', 688), ('KEY_MACRO_PRESET1', 691), ('KEY_MACRO_PRESET2', 692), ('KEY_MACRO_PRESET3', 693),
        ('KEY_KBD_LCD_MENU1', 696), ('KEY_KBD_LCD_MENU2', 697), ('KEY_KBD_LCD_MENU3', 698), ('KEY_KBD_LCD_MENU4', 699), ('KEY_KBD_LCD_MENU5', 700)
    ]
}

As you can see, it has no "normal" buttons or keys (indeed, I would suggest this is precisely the kind of peripheral for which input-mapper is ideally suited). However, the classifier in groups.py doesn't know what to make of this, classifies it as UNKNOWN and completely ignores it.

It would be nice to have a provision whereby I can say, "No no, this is a valid input device that generates valid events; please register it, anyway." This could be specified by USB vendor/product ID, the name registered with the kernel input system, or by whatever else is convenient for the program.