Drop support for gdal 1.X

Summary

This merge request removes support for GDAL 1.X.

Rationale

Gdal 2.X has been around for some time, and supporting both version is hard to maintain (see #1769 (closed)).

Modifications

The following modifications have been made :

• Change the required version of GDAL from 1.10 to 2.0 in Modules/ThirdParty/GDAL/otb-module-init.cmake
• tests on GDAL_VERSION_NUM for version prior to gdal 2.0 have been removed.
• The namespace otb::ogr::version_proxy has been removed, in particular :
  • the functions GetAvailableDriversAsStringVector, GetFileListAsStringVector(GDALDataset * dataset) and IsFieldSetAndNotNull have been moved to the otb::ogr namespace in the file otbOGRHelpers.h. Note that IsFieldSetAndNotNull still depends on GDAL version (one implementation for GDAL<2.2 and one for GDAL >=2.2).
  • All other functions of the namespace have been deleted and replaced by the GDAL 2.X equivalent, for example version_proxy::Open(...) have been replaced by GDALOpenEx(...)
• The CMake variable OTB_USE_GDAL_20 has been removed, as it is always true now.
• The minimum version of GDAL has been modified in the software guide.

Additional notes

Please tell me if you think I missed something that can be removed in this MR !

Copyright

The copyright owner is CNES and has signed the ORFEO ToolBox Contributor License Agreement.

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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
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