eeze/sensor: Switch timestamp to relative values coming.

eeze/sensor: Switch timestamp to relative values coming.

Switch from absolut microseconds since epoch to a monotonic clock with
realtive values. Switch from unsigned long long to double.

This aligns it with how we present time in efl. ecore_time_get is used
when possible. For the tizen modules we convert the the epoch timestamp
we get into a double. This is still a working monotone clock source.

As this will be released the first time with 1.8 we don't have any API
break here.