ViewModelProperties namespaces converted to static class properties.

[danbelcher-MSFT]

Fixes #305.

Description of the changes:

• Implement the OBSERVABLE_NAMED_PROPERTY class of macros. This macro will define the requested property as a member property and will additionally define a static class property that provides the name of the property as a string.
• Remove unused propertynames that were never used.
• For places where the source file still need the property name, e.g. to raise a property changed event or when internally checking for property change events, moved the property names to an anonymous namespace for the file.

How changes were validated:

• Manual. Unit tests pass locally.
• Smoke tests. Verify properties that were checked via code-behind, e.g. IsMemoryEmpty, still correctly functioned after the change.

[HowardWolosky]

@danbelcher-MSFT - Looks like recent merges have introduced conflicts. Can you sync/merge/push an update?