Details: Get static image data from our images services.

Details: Get static image data from our images services.

        * src/main/java/org/glom/web/client/ui/details/DetailsCell.java:
	Add constructors for LayoutItemText and LayoutItemImage and
	deal with their common type instead of just LayoutItemField.
        setData():
        * src/main/java/org/glom/web/client/activity/DetailsActivity.java:
       	Adapted.
        * src/main/java/org/glom/web/client/ui/details/Group.java:
        createChildWidget(): Use the other DetailsCell constructors for
	these layout items, and do not add them to the list of
	cells with data from the database.
        * src/main/java/org/glom/web/server/ConfiguredDocument.java:
        getValidListViewLayoutGroup(), getDetailsLayoutGroup():
	Remove the image data when cloning the layout and storing it in the
	cache. Clients will instead get it via the URL, from
	our images service.
        * src/main/java/org/glom/web/server/OnlineGlomImages.java:
	doGet(): Depending on the URI parameters, optionally get
	image data from a layout_item_image in the document,
	via its layout path.
        * src/main/java/org/glom/web/server/database/DBAccess.java:
        convertResultSetToDTO(): Move some URIBuilder code to:
        * src/main/java/org/glom/web/server/Utils.java:
	Add buildImageDataUrl() taking the primary key, etc, to
	get data from the database.