Fixes issue #35

There is a \todo below

Wifi MSDU and MPDU aggregation rework

See merge request nsnam/ns-3-dev!19

Hence, have them stored by the unique MacLow object

Also, remove m_ldpc and m_stbc, as they can be obtained via
the VHT capabilities, and m_shortGuardInterval, m_streams and m_greenfield,
as they can be obtained via the HT capabilities.

BasicEnergySource::UpdateEnergySource

See merge request nsnam/ns-3-dev!48

Otherwise remaining energy goes below zero.

Otherwise, if energy consumption is queried frequently, canceled events are produced.
These events take up memory and slow down the simulator.

Otherwise consumed energy may be estimated incorrectly if it is queried at the end of simulation.

core: (fixes #43) Check if ObjectFactory has been configured

Closes #43

See merge request nsnam/ns-3-dev!46