Minimal support for CNV analysis

Background

Implement minimal support for analysis of copy number variants (CNV) in ELLA, as first iteration for full support for structural variants (&2).

Implementation

Requirements (draft):

• Supported data: HTS (CNVs/dup/del only)
• Datamodel: Implement representation of CNVs, preferrably in the allele table
• UI elements/functionality:
  • Switch between viewing SNV (SMALL) and CNV (STRUCTURAL) in sidebar (skip ALL for now)
    • TBD: Size cutoff for small/structural variants. Do we need one, or just separate between variants called in different pipelines?
    • TBD: Decide which columns should be available in sidebar for STRUCTURAL in QUICK, FULL and VISUAL mode
  • Switch between CNV variants in the sidebar (same as for SNVs)
  • FULL mode: use existing layout/comment boxes
  • CNV tracks in VISUAL
• Filtering/prioritisation: Filtering left to upstream tools for now

Related issues

An important, additional feature is specified in #99 (closed) (links to existing allele assessments in VISUAL). #93 (closed) and #273 (closed) also needs to be done to support the many tracks relevant (and thereby track selector buttons) for CNVs.