Add Transcripts GnomadAD constraints and clinvar reports in the export

[incardon]

Is your feature request related to a problem? Please describe.
No

Describe the solution you'd like
Having in the export Transcripts, GnomAD constraints, and clivar reports

Describe alternatives you've considered
None

Additional context
No additional context

[incardon]

Implementation Proposal
RowWithTranscripts that wrap the result table in order to make the exporters working with the additional transcript columns.
load_molecular_impact moved in model.py to be usable in the exporter. Adding test with and without jannovar enables with mockers in the test.
Extend CaseExportTableQueryPartsBuilder with GnomAD constraints
Extend ProjectExportTableQueryPartsBuilder with GnomAD constraints

ExtendQueryPartsGnomadConstraintsJoin add additional fields: "oe_lof", "oe_lof_upper", "oe_lof_lower

Affected Components
Exports

Affected Modules/Files
variants/file_export.py, variants/models.py variants/tests/test_file_export.py factories.py variants/query.py

Required Architectural Changes
A RowWithTranscripts must be created

Implementation Sketch
Create a RowWithTranscripts following the design of RowWith*. All the other fields are in the query, so not need to extend with RowWithSomething.