[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-exif/v3/undefined/registration.go

@@ -1,42 +0,0 @@
-package exifundefined
-
-import (
-	"github.com/dsoprea/go-logging"
-)
-
-// UndefinedTagHandle defines one undefined-type tag with a corresponding
-// decoder.
-type UndefinedTagHandle struct {
-	IfdPath string
-	TagId   uint16
-}
-
-func registerEncoder(entity EncodeableValue, encoder UndefinedValueEncoder) {
-	typeName := entity.EncoderName()
-
-	_, found := encoders[typeName]
-	if found == true {
-		log.Panicf("encoder already registered: %v", typeName)
-	}
-
-	encoders[typeName] = encoder
-}
-
-func registerDecoder(ifdPath string, tagId uint16, decoder UndefinedValueDecoder) {
-	uth := UndefinedTagHandle{
-		IfdPath: ifdPath,
-		TagId:   tagId,
-	}
-
-	_, found := decoders[uth]
-	if found == true {
-		log.Panicf("decoder already registered: %v", uth)
-	}
-
-	decoders[uth] = decoder
-}
-
-var (
-	encoders = make(map[string]UndefinedValueEncoder)
-	decoders = make(map[UndefinedTagHandle]UndefinedValueDecoder)
-)