Switch accessories mapped on Home Center global variables.

It is possible to create Switch accessories on HomeKit with a toggle behaviour by:

1. creating global variables (one for each switch) with 2 possible values: "true" and "false"
2. configuring a new parameter ("switchglobalvariables") in config.json that contains a comma separated list of the variable names you defined.

You can use these variable to trigger Home Center scenes.

Known issue: you need to configure homebridge in config.json with a user with superuser privileges because normal users cannot set global variable from the outside of Home Center.