feat(annotation) added annotation tag type properties and annotation iteration keybinds

[chrisj]

Tags properties are currently represented as:

"annotationProperties": [
  {
    "id": "tag0",
    "type": "uint8",
    "tag": "a"
  }
]

Annotation layers now have a tag tab which displays the current tag properties and allows additional ones to be added. A tool is created for each tag which can be bound to a keybind like any other tool. The tools toggle the associated tag's status for the current selected annotation.

This feature also bundles keybinds to iterating through the currently selected layer's annotations. To do this, I added the concept of layer events and sendEventToSelectedLayer.