Annotation services

[eboileau]

Aims/objectives.

Annotation services are "split" into Ensembl and GtRNAdb, but the latter is only partly implemented, see #97

The exporter service is currently hard coded for Ensembl (and contains queries that should not be handled there).

A clear and concise description of todo items.

• Refactor annotation services (rely on FileService, cf. AssemblyService, to isolate tests)
• Refactor exporter service, cf. Data import/export implicitly assumes that specs are backward and forward compatible #150
• Which methods go to AnnotationService, which to FileService, which to Bedtools, ...

[eboileau]

If we end-up using both annotation, the source could come from the Browse View getApiUrl.