Feature #8725: simplification configurable

The simplification is configurable by layer, also this commit contains
reording of code.

I have pending show in the properties form of layer a check for
enable/disable the simplification

src/core/CMakeLists.txt

@@ -81,7 +81,6 @@ SET(QGIS_CORE_SRCS
   qgslabelattributes.cpp
   qgslabelsearchtree.cpp
   qgslogger.cpp
-  qgsmaprequest.cpp
   qgsmaplayer.cpp
   qgsmaplayerregistry.cpp
   qgsmaprenderer.cpp