Add refDepthDefaulted field to Well class.
Adapt tests to use new Well constructor, add test for defaulted ref depth.
Change Well constructors to avoid explicit bool arg.

Suggested by Joakim Hove.
Update checkWELSPECSConsistency() method.

Now accounts for new refDepthDefaulted() method and semantics.
Merge pull request #274 from atgeirr/default-wellrefdepth

Correctly handle defaulted well reference depths