end-to-end ujson integration

[lockefox]

Improve performance by making sure ujson is integrated everywhere in the stack it should be.

• incoming requests
• tinydb connections
• pandas to_json
  • pandas.io.json.dumps = ujson.dumps
  • pandas.io.json.loads = usjon.loads + precise_float=True in pd.read_json() args
• skip Flask.jsonify by building response directly from pandas

[lockefox]

Warning, ujson integration may cause heavy memory overhead