[FEATURE][processing] remove TauDEM provider from core Processing

TauDEM is quite specific set of tools and it requires installation of
some additional tools. So we decide to turn it into separate provider,
reducing core codebase size and maintenance efforts.

Tagged as feature to not forget mention in changelog and documentation

images/images.qrc

@@ -554,7 +554,6 @@
         <file>themes/default/providerGrass.svg</file>
         <file>themes/default/providerQgis.svg</file>
         <file>themes/default/providerR.svg</file>
-        <file>themes/default/providerTaudem.svg</file>
         <file>themes/default/processingModel.svg</file>
         <file>themes/default/processingScript.svg</file>
         <file>themes/default/processingAlgorithm.svg</file>

python/plugins/processing/algs/CMakeLists.txt

@@ -5,7 +5,6 @@ ADD_SUBDIRECTORY(gdal)
 ADD_SUBDIRECTORY(grass7)
 ADD_SUBDIRECTORY(saga)
 ADD_SUBDIRECTORY(otb)
-ADD_SUBDIRECTORY(taudem)
 ADD_SUBDIRECTORY(lidar)
 ADD_SUBDIRECTORY(qgis)
 ADD_SUBDIRECTORY(r)