Resolve "Add the possibility to activate both hillshade algorithm (classical + rastertools)"

I suggest the following workaround to deal with the activation of both hillshade methods :

1. if shaded is set to true in config, classic hillshade method is computed, written in a file and return as a mem variable
2. if rastertools is set to true in config, rastertools hillshade method is computed and written in a file
3. if both parameters are set to true in config, the classic hillshade mem variable is used as its mask + the rastertools written file is read then used as its mask -> Both masks are combined ( mask_classic OR mask_rastertools = final_mask) and the final mask is written