Add "hidden" property to status.

See merge request !74

Remove useless default params from property classes

See merge request !73

Use relative include path, fixes #15

Closes #15

See merge request !72

use internal_type_name in property_exists() instead of dynamic_cast

Closes #13

See merge request !71

Fix operator-- in some of the new iterators

See merge request !69

Found in compiler warning:

```
../Type-OpenVolumeMesh/libs/OpenVolumeMesh/src/OpenVolumeMesh/Core/Iterators.cc:1558:18: warning: equality comparison result unused [-Wunused-comparison]
        hf_iter_ == halffaces.end();
```

Halfedge vector and length

See merge request !67

Allow completely disabling deprecated APIs with CMake option OVM_ENABLE_DEPRECATED_APIS

See merge request !68

At some point in the future, we should switch the default to OFF.

Iterators

See merge request !65

Fixes

See merge request !20

More work on compiler warnings

See merge request !64

cmake compiler flag cleanup, enable many clang warnings and fix them

See merge request !63

Fix danging reference bug caused by halfedge().from_vertex().

See merge request !62

NormalAttrib: default props to 0 instead of undefined

See merge request !61

Implement type check in assignProperties()

See merge request !60

We should not return references to members of possible xvalues.
Handle is lightweight enough that copying is not a problem.

cppcheck fixes

See merge request !59