Extend 'units.sanitizer' function to replace omega character

The current implementation of the `units.sanitizer` function includes the 'micro' and 'mu' characters and replaces them with the 'u' character.

Since the large omega (Ω) is the symbol of the derived SI unit ohm, it might make sense to include it in the `sanitizer` and replace it with `Ohm`.

If not escaped, this breaks an import from a UTF-8 odML file containing the Ω character in a `Property.unit` to NIX using Python 2 with a `UnicodeDecodeError`.

Start by locating the `units.sanitizer` implementation and review how it handles the existing `micro` and `mu` characters. Verify that an odML import with Ω in `Property.unit` no longer raises a Python 2 `UnicodeDecodeError`, and that the character is converted to `Ohm`.

Written by the indexing model from the issue text.