Deprecate mapnik in 7.0
Summary
This MR improves the handling of deprecated features, and also deprecate Mapnik related modules.
Rationale
See #1692 (closed).
Implementation Details
CMake build system
- Improvements on the handling of deprecated modules. It is now possible to declare a whole module 
DEPRECATED. - If the option 
OTB_USE_DEPRECATED=OFF, this module will be disabled. - The modules export macros are now consistent (uppercase/lowercase). For instance 
OTBIOTileMapExport.hdefines:OTBIOTileMap_EXPORTOTBIOTileMap_DEPRECATEDOTBIOTileMap_DEPRECATED_EXPORT
 
Classes and files
- The Mapnik modules OTBMapnik and OTBVectorDataRendering are now deprecated
 
Documentation
Doxygen tags \deprecated have been added.
Additional notes
Copyright
The copyright owner is COPYRIGHT OWNER (OR OWNER'S AGENT) and has signed the ORFEO ToolBox Contributor License Agreement.
Check before merging:
- All discussions are resolved
 - At least 2 
👍 votes from core developers, no👎 vote. - The feature branch is (reasonably) up-to-date with the base branch
 - Dashboard is green
 - Copyright owner has signed the ORFEO ToolBox Contributor License Agreement
 
Edited  by Guillaume Pasero