Allow changing blind command in venetian mode

If you are using a FIbaro FGRM-222 in venetian blind mode, then I have to use 
`ASC_SlatPosCmd_SlatDevice: positionSlat`

But then we should better use "set xyz positionBlinds" instead of the dim command.

Blinds cmd: positionBlinds
Slats cmd: positionSlat

I've tried to fix it using the following eventMap without success:

`eventMap dim:positionBlinds`



