Show Pointer objects as links

**Is your feature request related to a problem? Please describe.**
Forte's new [pointer](https://github.com/asyml/forte/blob/master/forte/data/ontology/core.py#L427) objects standardize the connection between entries. Pointers can be the attributes of entires, the current Stave's main view does not support Pointers.

**Describe the solution you'd like**
A simple solution is to display Pointer objects as a link when displaying the attribute set, so a user can follow this link to jump to the relevant one. This solution may depend on https://github.com/asyml/stave/issues/59

**Describe alternatives you've considered**
Showing simply some identifier of the pointing object is possible, but not very informative.

**Additional context**
N/A

Start with Stave's main view and the attribute-set display, then review Forte's Pointer definition in forte/data/ontology/core.py. Check the related Stave issue #59 for the navigation dependency; done means Pointer attributes render as links that jump to the referenced entry.

Written by the indexing model from the issue text.