Intermediate visibility between public and private

[smedilol]

See #995 which was the proposal for a refactoring of visibility and namespace introduction. See (TODO create issue) for the meeting about this proposal.

Issue #1081 Public/Private visibility refactoring should be done before.

• [ ] #1046 namespace and using clause
  • Type and procedure can now be qualified with a namespace
  • Search of types and procedure without namespace qualification must use using clauses
• [ ] #1047 protected clause
• [ ] #1097 shared clause