Changes the type of the stored supported keywords from pointer-to-vector
to vector. This accomplishes the following:
* we avoid an unecessary level of indirection
* we enable initializer list syntax for tests etc.
* GridProperties' interface properly communicates that it takes over
ownership of the passed keywords.
* it feels more natural in use as generating and returning a vector in a
free function can be returned and directly passed to the constructor
(the motivation for this change).
Bundled with this is the move of the supported keyword population into
using loops to exploit the similarities of families of keywords w.r.t.
GridProperties representation.
5b2ec6be75