Fix #3804, Fix #5776

* Change animated GIF detection to not shell out to ImageMagick

Signed-off-by: Eugen Rochko <eugen@zeonfederated.com>

* Change video encoding parameters to limit to 10800 video frames

Signed-off-by: Eugen Rochko <eugen@zeonfederated.com>

* Limit GIF image size further

Signed-off-by: Eugen Rochko <eugen@zeonfederated.com>

* Always strip metadata from video files

* Fix code style issues

Resolve #11187

Also, because Chrome sends audio/mp3 instead of audio/mpeg as it's
supposed to, we need to whitelist that mime type as well

This replace calls of String#match? with rails Regex#match?
This follows the same idea used to keep Rails 5.2 compatible with Ruby
2.2.2 in https://github.com/rails/rails/pull/32973

While this isn't exactly *wrong*, files uploaded with a “.jpe” extension will
keep that extension, which will often cause them to be served with an
incorrect mimetype.

* Detect extension for preview card

* next