[!139] Removed data member vector::skip

Merge branch 'master' into 'master'

ref:staging/dune-uggrid Removed vector::skip and the code that uses it. It
compiles and the few existing tests run without problems.

Fixes [#29]

See merge request [!139]

  [#29]: gitlab.dune-project.org/NoneNone/issues/29
  [!139]: gitlab.dune-project.org/staging/dune-uggrid/merge_requests/139


Closes #29