gene.tsv output file empty when run using --prefix phenotype-only

[julesjacobsen]

In this case Exomiser should be producing an empty variant.tsv file (even when a VCF is provided) and just performing a phenotype profile match against the gene models in the database. This will produce a much worse result than when run using a VCF and a phenotype, so a warning should be given when this is done.

Exomiser will now only load an analyse a VCF when a variant-dependent analysis step is given in the analysis section, whereas previously it would load the VCF, but would not fully annotate it so would produce a sub-par analysis.

Exomiser would also happily produce no analysis at all when given no analysis steps to run. This should produce an error.