energy estimations of both sleep and deep sleep CPU modes.
Added configurable type ENERGEST_TIME_T to re-add support for clocks with
wrapping time as energest time source.
* energest time defaults to rtimer but can be configured via
ENERGEST_CONF_CURRENT_TIME and ENERGEST_CONF_SECOND.
* Additional energest types can be added by platform and application
using ENERGEST_CONF_PLATFORM_ADDITIONS and ENERGEST_CONF_ADDITIONS.
* Energest times are now 64 bit and thereby non-wrapping in most systems.
* Removed unused energest types for serial and sensors.
