Avoid leading slash in default MQTT topics

[xoseperez]

Originally reported by: Sven Kopetzki (Bitbucket: TriCX, GitHub: TriCX)

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According to HiveMQ MQTT Essentials the use of a leading forward slash should be avoided.

... It is allowed to use a leading forward slash in MQTT, for example /myhome/groundfloor/livingroom. But that introduces a unnecessary topic level with a zero character at the front. That should be avoided, because it doesn’t provide any benefit and often leads to confusion.
...

May I request to change the default MQTT topic generation without leading "/"?
It is also in conflict with most of the other home automatisation frameworks out threre.

Thanks!

[xoseperez]

As of 1.9.6 default base topic is "{identifier}" without leading slashes

[xoseperez]

Removing milestone: 1.9.6 (automated comment)