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.
flash files can be quite big (the biggest on danbooru.donmai.us being
68.6MB atm). Reading it and applying complex transformations twice seems
unnecessary.
MediaFile#dimensions is called twice - in #width and in #height but
it only works on the first call because the file is read to the end and
consumed the first time so when #read is called the second time it only
returns the empty string
* Move image thumbnail generation code to MediaFile::Image.
* Move video thumbnail generation code to MediaFile::Video.
* Move ugoira->webm conversion code to MediaFile::Ugoira.
This separates thumbnail generation from the upload process so that it's
possible to generate thumbnails outside of uploads.
* Use libvips instead of ruby-imagespec for reading dimensions of jpeg, png, and gif files.
* Copy the code for reading the dimensions of flash files from ruby-imagespec.
Fixes an incompatibility between ruby-imagespec and the rubocop gem that
prevented us from including rubocop in the Gemfile.
* Add MediaFile abstraction. A MediaFile represents an image or video file.
* Move filetype detection and dimension parsing code from uploads to MediaFile.
