Deep and external features
This MR address three points:
- A small fix in classification step where the external feature function was not correctly handled if DL is enabled
- Handle the case when a sampleExtraction output sqlite is empty if no reference data intersect the chunk
- Fix an issue which cause that extracted features are all set to 0 when using external features
A small doc was added containing warning about the external function labels and which data are used.
Edited by Tardy Benjamin