Added Java EPUB validator (and its dependencies). Fixed the following
errors reported by the validator:

C:\...>java -jar test\epubcheck-3.0b5.jar 52c0423c4d45f2ac15000005.epub
Epubcheck Version 3.0b5

Validating against EPUB version 2.0
ERROR: 52c0423c4d45f2ac15000005.epub/OEBPS/content.opf(4,50): The prefix
"opf" for attribute "opf:scheme" associated with an element type
"dc:identifier" is not bound.
ERROR: 52c0423c4d45f2ac15000005.epub/OEBPS/content.opf: The prefix "opf"
for attribute "opf:scheme" associated with an element type "dc:identifier"
is not bound.
ERROR: 52c0423c4d45f2ac15000005.epub/OEBPS/content.opf: unique-identifier
attribute in package element must reference an existing identifier element
id

Check finished with warnings or errors
Run EPUB validator from IT. This reported the errors below which have been
fixed.

```
C:\Users\mgf\Dropbox\Dokumenter\Udvikling\Kode\Scripler\Github\Scripler\scripler>java
-jar test\epubcheck-3.0b5.jar 52c048c0818f03f020000005.epub
Epubcheck Version 3.0b5

Validating against EPUB version 2.0
ERROR: 52c048c0818f03f020000005.epub/OEBPS/content.opf(8,62): date value
'1388333248564' is not valid as per
http://www.w3.org/TR/NOTE-datetime:[For input string: "1388333248564"] is
not an integer
ERROR: 52c048c0818f03f020000005.epub/OEBPS/content.opf(22,117): value of
attribute "id" is invalid; must be an XML name without colons
ERROR: 52c048c0818f03f020000005.epub/OEBPS/content.opf(34,46): value of
attribute "idref" is invalid; must be an XML name without colons
ERROR: 52c048c0818f03f020000005.epub/OEBPS/content.opf(22,117): assertion
failed: The "id" attribute does not have a unique value
ERROR: 52c048c0818f03f020000005.epub/OEBPS/content.opf(39,63): File listed
in reference element in guide was not declared in OPF manifest:
OEBPS/Cover.html
ERROR: 52c048c0818f03f020000005.epub/OEBPS/content.opf(28,118):
non-standard media-type 'application/x-font-ttf' with no fallback
ERROR: 52c048c0818f03f020000005.epub: OPS/XHTML file
OEBPS/HTML/52c048c0818f03f02000000b.html is missing
ERROR: 52c048c0818f03f020000005.epub: image file
OEBPS/Images/52c048c0818f03f02000000b.jpg is missing
ERROR: 52c048c0818f03f020000005.epub: resource
OEBPS/Fonts/52c048c0818f03f02000000b.tff is missing
ERROR: 52c048c0818f03f020000005.epub: resource OEBPS/Scripler-license.txt
is missing
WARNING: 52c048c0818f03f020000005.epub: item (OEBPS/HTML/A New Cool
Name.html) exists in the zip file, but is not declared in the OPF file
WARNING: 52c048c0818f03f020000005.epub/OEBPS/HTML/A New Cool Name.html:
Filename contains spaces. Consider changing filename such that URI
escaping is not necessary
ERROR: 52c048c0818f03f020000005.epub/OEBPS/content.opf(39,63):
'OEBPS/Cover.html': referenced resource missing in the package

Check finished with warnings or errors
```

Also:

* Send real XML (HTML) such to pass EPUB validation.
* Implemented Allan's review comments, except for comment about multiple authors which might require a) discussion with product owner (David) or b) rewriting the code to generate XML/HTML via a library.
* Changed ITs that open folders to not test exact returned index of documents and folders, since this is currently not guaranteed by the server (Folder.Open()).