added dimmer property to dmx_universe

A dimmer has been added to each universe. It dims all channels
linearly from 0-255, where 255 yields whatever the channel
currently holds (no change).
Example: Setting the dimmer to 127 will output 50% of each channel value
in this universe.

Signed-off-by: Maximilian Güntner <maximilian.guentner@gmail.com>
renamed dmx_set_universe_state to be consistent with other functions

Signed-off-by: Maximilian Güntner <maximilian.guentner@gmail.com>
Use uint8_t when parsing each channel value

We only store 8-bit values in dmx-storage and
we should parse the ecmd parameters according to
that.

Signed-off-by: Maximilian Güntner <maximilian.guentner@gmail.com>
Merge pull request #288 from mguentner/storage-master

DMX-Storage changes