Add Term Details to Post Response

Added general function to modify taxonomy response for all registered taxonomies returned by REST API (/wp-json/wp/v2/posts). Format:

"{taxonomy}": [
  {
    "term_id": {int},
    "name": {string},
    "slug": {string},
    "term_group": {int},
    "term_taxonomy_id": {int},
    "taxonomy": {string},
    "description": {string},
    "parent": {int},
    "count": {int},
    "filter": {string}
  },
  {
    "term_id": {int},
    "name": {string},
    "slug": {string},
    "term_group": {int},
    "term_taxonomy_id": {int},
    "taxonomy": {string},
    "description": {string},
    "parent": {int},
    "count": {int},
    "filter": {string}
  }
]