Merge branch 'coordinates-constructors-should-take-domain-size' into 'master'

This patch changes the semantics of the constructors of EquidistantCoordinates
and EquidistantOffsetCoordinates. Whereas previously they took the element
size, with the patch they now take the upper right corner of the domain.

Rationale: as of 067abb55 , Coordinates
objects can be used to construct YaspGrid objects. However, YaspGrid
constructors expect the upper right domain corner rather than the element
size. I think being consistent here will help to avoid many mistakes.

Technically, this commit is an interface change. However, I propose to
fast-track it because while users could use the constructors of the
Coordinates objects before 067abb55 , they
couldn't actually do anything with these objects. Therefore I argue that the
constructors are not really public API after all.

See merge request [!307]

  [!307]: gitlab.dune-project.org/core/dune-grid/merge_requests/307