scan-registers: determine available notifications

00 is documented in HID++ 1.0 specification, it should be safe to set the 00
register. As another program may have written the notifications register
already and since enabling notifications has side-effects such as "disabling"
certaing functions, restore the flags after reading out available notifs.
window popup fix for kwin

also, only try to position the window next to the status icon if it has never
been shown before
minor tweaks
re-work the status icon updating
version and url fixes
status icon menu items open the right device window
debian version update
Merge pull request #41 from Lekensteyn/tool-updates

scan-registers: determine available notifications
enable notifications for peripherals; fixes #27
only enable certain notification flags on devices

Also added some documentation to the notification flags, where possible.
minor readme update
only notify on connected devices at start-up
pop up a desktop notification if the battery is below 5%
depend on gnome-icon-theme or oxygen-icon-theme

It's necessary to make sure all the standard icons are available.
don't crash when failing to load the icon mask
version 0.8.8.1
about window tweak
hid10: document notifications better

See [registers.txt][1] for 'keyboard_backlight'. The behavior of
keyboard_sleep_raw and keyboard_multimedia_raw is described at
[keyboard.txt][2].

 [1]: https://git.lekensteyn.nl/ltunify/tree/registers.txt
 [2]: https://git.lekensteyn.nl/ltunify/tree/keyboard.txt
hid10: Formatting and re-order NOTIFICATION_FLAGs

Align values for easier reading the numeric values of NOTIFICATION_FLAGs.  To
maintain consistency in the ordering of the values, swap keyboard_backlight with
keyboard_present.
hid10: update flags description for notifications

The Logitech HID++ 1.0 documentation actually names the fields for devices and
receiver. Clarify that and explain why enabling all of the bits is a bad idea.