DISCO: import data for miRBase

NIF id: nif-0000-21267

• need to change resource url to http://www.mirbase.org/
• should be importing from
  should be importing from ftp://mirbase.org/pub/mirbase/CURRENT/database_files where the current release is 19
  see table definitions at ftp://mirbase.org/pub/mirbase/19/database_files/tables.sql
• mirna_species
• mirna_context
• mirna
• experiment
• mirna_database_links
• mirna_mature
• mirna_2_prefam
• mirna_target_links