sim: allow new service request states over gui

sim: allow new service request states over gui

Change the old enabled/disabled GTK "Switch" element to a ComboBox
one and add all possible service states, so we can simulate the real
world behaviour with its new states better.

As we do not need to map a the boolean swicth value to our states
anymore, we may drop the set_setvice_state method from the RTHardware
class and use the one from the Hardware base class instead.

Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>