Handle seat version 6

[elinorbgr]

We currently only handle the wl_seat global up to version 4. Versions 5 and 6 add significant logic needs:

version 5

This one add detailed logic to the axis events for wl_pointer

• wl_seat.release
• wl_pointer.frame
• wl_pointer.axis_source
• wl_pointer.axis_stop
• wl_pointer.axis_discrete

version 6

This one mostly adds touch-related events, and thus is blocked on #48 anyway.

• enum wl_pointer.axis_source.wheel_tilt (thus must not be sent to v5 clients !)
• wl_touch.shape
• wl_touch.orientation

[Drakulix]

Version 5 is fixed as of #83