Fixes r.horizon - ticket #6760 and fixes #7344 (spaces need to be escaped when passing parameters to GRASS modules)

GRASS r.horizon was not producing any output because it was missing the necessary field. It was anyway needed to remove the "horizonstep" parameter because using this GRASS will create >1 output and as far as I know this is not yet supported in processing. Even when creating just one output the module adds a "_0" suffix to it, so it was needed to patch GrassAlgorithm.py. I add also a "r.horizon.height" module to support the module 2nd way to work, that produces an output just in the GRASS log.