re #fix_5 edit lib.rs to be used with DBEntry and not String anymore

re #fix_5 the HashMap of the database is now an array of DBEntity
objects and not an array of String

re #fix_5 add dbentity in mod.rs

re #fix_5 add dbentry structure who contains the sinograms and frequency
of one entry in database

re #fix_5 delete useless code

re #fix_5 update the dbentry structure : add a new() method
re #fix_5 get the frequency of one sinogram from the database

re #fix_5 fix entry copy problem
re #fix_5 change structure name

re #fix_5 update the dbentry structure name and refractor code

re #fix_5 delete unused module