Release 3.1

Closes #17, #15, and #19

See merge request remi.cresson/otbtf!24

Resolve "gdal import (python)"

See merge request remi.cresson/otbtf!20

Resolve "PatchesSelection: add the possibility to specify proportions/datasets custom names"

See merge request remi.cresson/otbtf!19

ENH: remove RejectPatchesWithNodata. Same logic as PatchesSelection: if the user specifies the NoData, then we reject patches with NoData, otherwise not
ENH: overload PushBackInputWithPatchSize to make nodata optional