encap: Remove 'scalar' from Encapsulation.

Previously the `Encapsulation` class had a `setval` method that accepted a `scalar` (which was a template variable).  This was unnecessary, as the only usage of `setval` was `setval(0.0)`.  As such, `setval` was replaced by `zero`, and hence `scalar` can be removed from the `Encapsulation` altogether.

This leads me to consider replacing `time` in `Encapsulation` by `double`.  There is already precedent for this in `Controller`.  Perhaps a better solution would be to have a configuration variable to define the precision used for `time` throughout.