Support DataFrame indexing with mars Tensor

[MaxwellLZH]

Currently the following snippets causes error, which is quite surprising for users coming from Pandas background:

import mars.dataframe as md
import mars.tensor as mt
df = md.DataFrame(mt.random.randn(10, 4))
df.loc[df.index].execute()

It will be nice to support indexing with Mars Tensor as well.

Thank you !

[qinxuye]

Thanks, will support it ASAP.

[MaxwellLZH]

Wondering if the issue has been fixed in the newest version?