Allow non "homie/" prefix in online validation tool

[CamDavidsonPilon]

IIUC, the "homie/" prefix can be changed to "X/" for branding reasons

If this root topic does not suit your needs (in case of, e.g., a public broker or because of branding), you can choose another.

However, the online validator will fail if this is changed:

reactor/device123/$homie 4.0
reactor/device123/$name My device
reactor/device123/$state ready
reactor/device123/$extensions 
reactor/device123/$nodes mythermostat

reactor/device123/mythermostat/$name My thermostat
reactor/device123/mythermostat/$properties temperature

reactor/device123/mythermostat/temperature 22 
reactor/device123/mythermostat/temperature/$name Temperature
reactor/device123/mythermostat/temperature/$unit °C
reactor/device123/mythermostat/temperature/$datatype integer

Fails with

Must begin with homie/

[CamDavidsonPilon]

Whoops, this is a better issue for the website repo. Closing and moving there.