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 to replacing `time` in `Encapsulation` by `double`.  There is already precedent for this in `Controller`.  The use can still redefine the 'time' precision by tweaking 'config.hpp'.