Tiles and maps built with the map factory framework should report progress

[david-rhodes]

As a developer, I should know when a tile is finished loading (from the web), as well as any post-processing that happens after the tile is fetched (texture generated, meshes built, etc.). This will help to create animations, avoid temporal coupling, and allow for loading screens, etc.

[david-rhodes]

First pass progress reporting has been implemented: #89.

The AbstractMap has an initialized event, but this is used for doing conversions that require specific map attributes (reference tile and world scale, etc.). The MapVisualizer now has state changed events, as well as all the TileFactories. Use these to know when specific factories, or the entire map are done loading.