adding help_text and better string representation for model fields
adding help_text and better string representation for model fields

tndatacommons/tndata_backend,izzyalonso/tndata_backend,izzyalonso/tndata_backend,izzyalonso/tndata_backend,tndatacommons/tndata_backend,izzyalonso/tndata_backend,tndatacommons/tndata_backend,tndatacommons/tndata_backend