Streamable keys added back in graph_objs_meta.{py,json}

* streamable=True added back for streamable keys:
'x','y','z','text','marker' ('size', 'color').

Urgent as `py.Stream.write()` validates streamable keys. 

In v.1.0.32
```
py.Stream.write(dict(x=my_x,y=my_y)) 
```

Throws a validation error. 

* Also, 'boxmode' description made consistent with 'barmode'.