SciberQuestToolKit -- CUDA build issues

This patch fixes the build issues introduced in the recent
refactoring so that CUDA filters can again be used.

Change-Id: I42cdafcdb2ce8a8c54abc46688dc306e4c04b937
SciberQuestToolKit -- I/O features

Added dt to metadata for series with fixed timestep
Added support for extensions other than gda in the
metadata (ext=...)

Change-Id: I9f84eb85dd4a2bee45c0e87fb1fa0679233dae05
Merge topic 'sqtk-refactor-fixes' into next

b5fcb78b SciberQuestToolKit -- I/O features
1d0adc0e SciberQuestToolKit -- CUDA build issues