Loading and Error Screens

[ryan-berger]

Right now the loading bar stays out of the way when loading the longest line of sight for a tile.

Sometimes it can be seen at the top after clicking on a line of sight, but it allows the user to roam around.

When jumping to a location via URL an overlay is shown and no loading bar is visible.

If, in the overlay state, some non 200 status codes occur out then the entire site hangs. This generally won't happen in production with our full maps, but we probably want to make sure we at least stop loading the line of sight and display an error message so the user can continue to use the site.

I think the should loading take more than a second, we should pop up an overlay/loading screen to force them to wait. Once we're finished we can hop them into the line of sight they clicked in, or the coordinate they typed into the URL.

[tombh]

I think the errors were mostly being cause by #42. I still think we need to handle errors, but perhaps this is lower priority now? It would be good to have an error case to reproduce with.