Refactor of experiment->target

[sveinugu]

Added subproperties of target:

• sequence_feature
• gene_id
• gene_product_type
• macromolecular_structure
• phenotype
• target_details

In addition, I have added checks on relations between technique and required subproperties, as well as specific constants to use, for various common techniques:

• histone modification identification by ChIP-Seq assay -> sequence_features required
• bisulfite sequencing assay -> sequence_features=open_chromatin_region
• DNase I hypersensitive sites sequencing assay -> sequence_features=DNAseI_hypersensitive_site
• transcription factor binding site identification by ChIP-Seq assay -> gene_product_type=Transcription Factor, gene_id required
• RNA-seq assay -> gene_product_type=Messenger RNA
• microRNA profiling by high throughput sequencing assay -> gene_product_type=MicroRNA
• Hi-C assay -> macromolecular_structure=Chromatin Structure
• GWAS study -> phenotype required

"target" is now meant to be autogenerated based upon the subproperties, e.g. like "[relevant subproperty value] ([target_details])"

[sveinugu]

Solves https://github.com/fairtracks/fairtracks_standard/issues/11