GH-16: Update doc of how to implement Z-Wave CC

[silabs-borisl]

unify_host_sdk_documentation.zip SiliconLabs ref : GWAPPS-47

First draft of how to implement a Z-Wave command class :

• Definition and registration of attributes
• Implementation of get/set/report
• UAM files integration
• Unit testing

Built documentation available in attachments

The documentation can found at : applications/zpc/how_to_implement_zwave_command_classes.html (or search for zwave command class).

[rzr]

Please rebase and close if content is aligned