* Default dimmable brightness to 255 from 100
Full brightness for ISY dimmers is 255. The current 100 value turns dimmer switches on to just under half brightness. Probably just an oversight from the Sept implementation.
* Brightness change for turn_on, ramp for turn_off.
Per discussion with Teagan42 and jbcodemonkey, the brightness should rightfully be None and not an explicit value. There is a continuing issue that the ISY modules don't respect HA's brightness customization values. A new issue will be opened for this.
Additionally, turn_off was using ISY's fastoff() which didn't respect the ramping time. The default behavior should just be off().
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