Add support for Show/Hide

[dotasek]

Add support for Show/Hide

This requires several endpoints.

The first is the data representation, likely in Network Views, to represent individual objects and their settings:

• [x] GET /v1/networks/{networkId}/views/{viewId}/{objectType}/{objectId} should have some access to visibility.

The second possibly belongs under the v1/apply area, and should provided automated hiding for sets of nodes/edges. Not certain whether or not this should follow the GUI pattern of using the GUI selection, as that is definitely stateful, and it would be more flexible to pass selections to hide/show directly from Python as lists.

Batch hide/show (see #73) Note: Batch/hide show creeps the scope of this issue, so I removed it as a requirement for this issue.

[dotasek]

Already supported for individual graph objects. The visual properties that define this:

 {
    "visualProperty": "NODE_VISIBLE",
    "value": false
  }

 {
    "visualProperty": "EDGE_VISIBLE",
    "value": false
  }