directory structure change to work with glide

glide has its own requirements. My previous workaround caused me some
code checkin errors. Need to fix this.

weed/images/preprocess.go

@@ -0,0 +1,27 @@
+package images
+
+import (
+	"path/filepath"
+	"strings"
+)
+
+/*
+* Preprocess image files on client side.
+* 1. possibly adjust the orientation
+* 2. resize the image to a width or height limit
+* 3. remove the exif data
+* Call this function on any file uploaded to SeaweedFS
+*
+ */
+func MaybePreprocessImage(filename string, data []byte, width, height int) (resized []byte, w int, h int) {
+	ext := filepath.Ext(filename)
+	ext = strings.ToLower(ext)
+	switch ext {
+	case ".png", ".gif":
+		return Resized(ext, data, width, height)
+	case ".jpg", ".jpeg":
+		data = FixJpgOrientation(data)
+		return Resized(ext, data, width, height)
+	}
+	return data, 0, 0
+}