[feature] support processing of (many) more media types (#3090)

* initial work replacing our media decoding / encoding pipeline with ffprobe + ffmpeg

* specify the video codec to use when generating static image from emoji

* update go-storage library (fixes incompatibility after updating go-iotools)

* maintain image aspect ratio when generating a thumbnail for it

* update readme to show go-ffmpreg

* fix a bunch of media tests, move filesize checking to callers of media manager for more flexibility

* remove extra debug from error message

* fix up incorrect function signatures

* update PutFile to just use regular file copy, as changes are file is on separate partition

* fix remaining tests, remove some unneeded tests now we're working with ffmpeg/ffprobe

* update more tests, add more code comments

* add utilities to generate processed emoji / media outputs

* fix remaining tests

* add test for opus media file, add license header to utility cmds

* limit the number of concurrently available ffmpeg / ffprobe instances

* reduce number of instances

* further reduce number of instances

* fix envparsing test with configuration variables

* update docs and configuration with new media-{local,remote}-max-size variables

vendor/github.com/dsoprea/go-utility/v2/filesystem/utility.go

@@ -1,17 +0,0 @@
-package rifs
-
-import (
-	"io"
-	"os"
-
-	"github.com/dsoprea/go-logging"
-)
-
-// GetOffset returns the current offset of the Seeker and just panics if unable
-// to find it.
-func GetOffset(s io.Seeker) int64 {
-	offsetRaw, err := s.Seek(0, os.SEEK_CUR)
-	log.PanicIf(err)
-
-	return offsetRaw
-}