OLA – APA102 PixelBrightness support

video from the working thing:

long standing ‘ToDoList entry’ ­čÖé
some time back i added APA102 support to the olad spi plugin

back then i hardcoded the PixelBrightness (in the datasheet ‘global brightness’) to full.
Its an value from 0..31.
now i found time and added the missing code so you can choose the old 3ch per led or the new 4ch per led mode. so its possible to dim the strip down and still use the 3x8bit color range..

this pull request should be merged in some days..