Support for multiple versions of VEP annotation

The database schema has been heavily modified to support multiple versions of the Variant Effect Predictor (VEP) annotation. During the load of a VCF file, it is possible to annotate those variants using an existing or new version. The job that allowed to annotate already loaded studies or a whole database has been also modified accordingly.

The introduced database changes are:

• The bulk of the 'annot' subdocument in the variants collection has been extracted to the 'annotations' collection
• The variants collection only stores those fields used as indexes for efficient filtering
• New 'annotationMetadata' collection introduced, listing the versions of VEP used to annotate the variants in the database

If you had been using a previous version of this software, please check out the eva-tools repository in order to obtain the database migration scripts.