Add list of needed metadata.

Add list of needed metadata.

docs/metaitems.txt

+* Metadata on a directory
+** background image
+
+** background color (can be a ramp)
+
+** background ramp direction (h or v)
+
+** position and size of window
+
+** actions for "index view"
+
+** Preferred view name
+
+* Metadata for an item
+** position of icon
+
+gnomad had bounding box (x, y, width, height)
+
+** width and height of icon (allows stretching each icon)
+
+** image URL for icon (overrides the default)
+
+** list of images / parameterized image for icon that looks different at different zoom levels
+
+** user level at which the item becomes visible (it's invisible at lower user levels)
+
+** list of keywords that item has been tagged with (includes things like "archived")
+
+** notes
+
+** vault path for use in vault synchronization
+
+** last known fingerprint (MD5 sum) for use in vault synchronization
+
+** flag that specifies a particular item is non-draggable
+
+** Media files
+*** Title
+*** Artist
+*** Cover image
+
+* Global prefs
+** Current user level
+
+** Open-in-new-window