neuroglancer "common action" buttons

[stuarteberg]

Let's add some buttons (or possibly a drop-down menu, or possibly a "hamburger menu") to the page when neuroglancer is visible. Each "action" will modify the neuroglancer state in some predefined way.

Examples:

• Reset the position/orientation to the standard brain view
• Reset the position/orientation to the standard VNC view
• Toggle synapses on/off
• Toggle ROIs on/off
• Switch from meshes to skeletons
• Show available layers (the archived layer list)

Each action will be specified via a snippet of JSON which will be inserted into the neuroglancer JSON state. The list of actions and their associated JSON snippets will be provided via a new property in the :Meta node.

In the case of top-level settings, integrating them in the neuroglancer state is straightforward:

{
  "position": [
    48205.85546875,
    24408.794921875,
    26808.501953125
  ],
  "projectionOrientation": [
    0.19000111520290375,
    0.1747802048921585,
    -0.03336048871278763,
    0.9655250310897827
  ],
  "projectionScale": 115206.87860044689
}

In the case of items in the layers list, special logic will be needed. We'll require that the layer name is included in the snippet, and neuprintExplorer will locate the item in the neuroglancer layers JSON to modify. (The order of the layers will not be changed.)

"layers": [
  {
      "name": "brain-neuropils",
      "visible": true
  }
]

[neomorphic]

I have created a menu with the following options hard coded:

• Reset the position/orientation to the standard brain view
• Reset the position/orientation to the standard VNC view
• Toggle synapses on/off
• Toggle ROIs on/off

I am not sure how one would toggle between meshes and skeletons, but that shouldn't be hard to implement based on the reference handlers that I have added to the code.