CORE-6278 Fix for Reference Genome default values in Apps.

Updated metadactyl.metadata.params/get-default-value to use a new format-reference-genome-value function for Reference Genome/Annotation/Sequence parameter types, so that default reference genome values are correctly returned for the GET /apps/:id endpoint.
Refactored metadactyl.zoidberg.app-edit/format-default-value to also use the new metadactyl.metadata.params/format-reference-genome-value function.