Massive rework of platform layer user/organization

The goal of this rework is to make it so I can pass around platform.User
instead of a pair of models.Organization and models.User. This is useful
for reason I kind of forget now, but it started with working on
notifications and ballooned massively from there into refactoring a
number of things that were bugging me.

This also includes a tiny amount of work on server-side events (SSE).

 * background stuff lives inside the platform now, which I need for
   having it push updates through SSE
 * userfile now lives in the platform, under file, so other platform
   functions can safely use it
 * oauth is broken into pieces and inside platform because other stuff
   was calling it already, but badly.
 * notifications go into the platform as well

platform/file/base.go

@@ -0,0 +1,100 @@
+package file
+
+import (
+	"fmt"
+	"io"
+	"net/http"
+	"os"
+
+	"github.com/Gleipnir-Technology/nidus-sync/config"
+	"github.com/google/uuid"
+	//"github.com/rs/zerolog/log"
+)
+
+func audioFileContentWrite(audioUUID uuid.UUID, body io.Reader) error {
+	return nil
+}
+
+var collectionToExtension map[Collection]string = map[Collection]string{
+	CollectionAudioNormalized: "ogg",
+	CollectionAudioRaw:        "raw",
+	CollectionAudioTranscoded: "ogg",
+	CollectionCSV:             "csv",
+	CollectionLogo:            "png",
+	CollectionPublicImage:     "img",
+	CollectionImageRaw:        "raw",
+}
+var collectionToSubdir map[Collection]string = map[Collection]string{
+	CollectionAudioNormalized: "audio-normalized",
+	CollectionAudioRaw:        "audio-raw",
+	CollectionAudioTranscoded: "audio-transcoded",
+	CollectionCSV:             "csv",
+	CollectionLogo:            "logo",
+	CollectionPublicImage:     "public-image",
+	CollectionImageRaw:        "image-raw",
+}
+
+func ContentPath(collection Collection, uid uuid.UUID) string {
+	return fileContentPath(collection, uid)
+}
+func fileContentPath(collection Collection, uid uuid.UUID) string {
+	subdir, ok := collectionToSubdir[collection]
+	if !ok {
+		panic(fmt.Sprintf("No subdir for collection %d", int(collection)))
+	}
+	extension, ok := collectionToExtension[collection]
+	return fmt.Sprintf("%s/%s/%s.%s", config.FilesDirectory, subdir, uid.String(), extension)
+}
+
+/*
+	func fileContentWrite(body io.Reader, subdir string, uid uuid.UUID, extension string) error {
+		// Create file in configured directory
+		filepath := fileContentPath(subdir, uid, extension)
+		dst, err := os.Create(filepath)
+		if err != nil {
+			log.Error().Err(err).Str("filepath", filepath).Msg("Failed to create file")
+			return fmt.Errorf("Failed to create file at %s: %v", filepath, err)
+		}
+		defer dst.Close()
+
+		// Copy rest of request body to file
+		_, err = io.Copy(dst, body)
+		if err != nil {
+			return fmt.Errorf("Unable to save content of %s: %v", filepath, err)
+		}
+		return nil
+	}
+*/
+func writeFileContent(w http.ResponseWriter, image_path string) {
+	// Open the file
+	file, err := os.Open(image_path)
+	if err != nil {
+		if os.IsNotExist(err) {
+			http.Error(w, "Image not found", http.StatusNotFound)
+		} else {
+			http.Error(w, "Failed to retrieve image", http.StatusInternalServerError)
+		}
+		return
+	}
+	defer file.Close()
+
+	// Get file info for Content-Length header
+	fileInfo, err := file.Stat()
+	if err != nil {
+		http.Error(w, "Failed to get image information", http.StatusInternalServerError)
+		return
+	}
+
+	// Set appropriate headers
+	w.Header().Set("Content-Type", "image/png")
+	w.Header().Set("Content-Length", fmt.Sprintf("%d", fileInfo.Size()))
+
+	// Copy file contents to response writer
+	_, err = io.Copy(w, file)
+	if err != nil {
+		// Note: At this point, we've already started writing the response,
+		// so we can't change the status code anymore. The best we can do
+		// is log the error and abandon the connection.
+		return
+	}
+}