Document: Load static text and image items too.

Document: Load static text and image items too.

        * src/main/java/org/glom/web/shared/libglom/layout/LayoutItemImage.java:
        * src/main/java/org/glom/web/shared/libglom/layout/LayoutItemText.java:
	New LayoutItem classes to represent these layout items.
        * src/main/java/org/glom/web/shared/libglom/layout/StaticText.java: The
	main text of a LayoutItemText.
        * src/main/java/org/glom/web/server/libglom/Document.java:
        load_after_layout_group(): Handle the node types and instantiate the
	new classes.
        * src/test/java/org/glom/web/server/libglom/DocumentTest.java:
	Add testLayoutItemText() to check that the text is loaded properly.