Fix bug where map wasn't always setting for new sightings.

Apparently when uploading a sighting photo with GPS coordinates, the
coordinates were being extracted as expected but the map was not
automatically moving to the location. (#566)
Preserve size of smaller images when uploading.

The server resizes large-size images during upload to a size large
enough for use on web pages. It now preserves the size of smaller
images that are uploaded, instead of resizing to the larger
web-ready size. (#566)
Show some feedback during the wait after picking an image.

Known issue: the spinner animation usually gets blocked while
the browser reads the image file. (#566)
Enable the Upload button only when ready.

Before, the Upload button would be enabled before the thumbnail was
read and displayed. (#566)
Allow disabled image dialog buttons to be visible. (#566)
Wait a bit before resizing a newly loaded image.

There is a bit of a delay in getting the newly loaded image into
the element from which it will be resized, so compensate. (#566)