Use ExifTool to get the dimensions of Flash files instead of calculating
it ourselves. Avoids copying third-party code.
Fixes a bug where Flash files with fractional dimensions (e.g. 607.6 x 756.6)
had their dimensions rounded down instead of rounded up.
Fixes another bug where Flash files could return negative dimensions.
This happened for two files:
* https://danbooru.donmai.us/media_assets/228662 (-179.2 x -339.2)
* https://danbooru.donmai.us/media_assets/228664 (-179.2 x -339.2)
Now we round these up to 1x1. This is still wrong, but it's less wrong than before.
Don't wrap the metadata refresh script in a transaction because it could
be a very long running operation and it's not good to leave a transaction
open that long.
Add a script to go through every media asset and check the metadata
(width, height, duration, filesize, md5, EXIF metadata) and update it
if it's changed. This is necessary after upgrading ExifTool because the
metadata it returns may have changed.