Store EBI submission files with the preprocessed data

[josenavas]

Currently the files are stored in the working directory. However, the database don't keep track of any of those files. Since all these files are stored in a single directory, we can store such directory under the preprocessed_data mount point and link the EBI submission files to the preprocessed data (since there is a 1-1 relationship).

Assigning to @antgonza since he is currently working on the EBI refactor.