DATACMNS-1315 - Added a cover page for epub output.

I added a cover page for the epub output, now that the Spring data reference guides will have epub output (through a commit against spring-data-build).

Original pull request: #290.

Author: Jay Bryant

src/main/asciidoc/images/epub-cover.png

@@ -5,11 +5,12 @@ Oliver Gierke; Thomas Darimont; Christoph Strobl; Mark Pollack; Thomas Risberg;
 :linkcss:
 :doctype: book
 :docinfo: shared
-:toc:
+:toc: left
 :toclevels: 4
 :source-highlighter: prettify
 :icons: font
-
+:imagesdir: images
+ifdef::backend-epub3[:front-cover-image: image:epub-cover.png[Front Cover,1050,1600]]
 
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