Upgrade to Gradle 1.6 and resolve deprecations

Before this change, Spring shared Gradle plugins were using Gradle 1.1.
Recently Spring core framework build started using Gradle 1.6. New
Gradle has deprecated several APIs which were used in Spring shared
Gradle plugins, resulting in deprecation warnings being printed in
Spring framework build output itself.

This patch upgrade Gradle to 1.6, and replaces usage of deprecated
Gradle APIs in Spring shared Gradle plugins.

This patch also includes upgrade of Gradle Artifactory Plugin (GAP) to
latest released version, 2.1.0. Unfortunatelly that plugin also uses
deprecated Gradle APIs, but to a lesser extent. When GAP-144 is
resolved, dependency on GAP should be further upgraded.

When merging this patch, please make sure that GAP 2.1.0 release is
available on springsource plugins-release repository.

Issue: GRADLE-53
Update gradle wrapper task to 1.6
Update CSS to improve Table of Contents layout

Tweak CSS to improve the table of contents to help the reader scan the
document more quickly.

Thanks to Ethan Andrews for the suggestion.
Reference Plugin: Make property sourceFileName configurable

* Add ability to completely disable property placeholder expansion
Update README.md
Merge pull request #17 from watsoncj/patch-1

# By Casey Watson
# Via Casey Watson
* patch-1:
  Update README.md
set width for div.preface
Next development version
[artifactory-release] Next development version
Hide 'revhistory' element

Hide the revision history element from default generated output. This
change allows docbook files generated from asciidoctor to render nicely.
Upgrade to Gradle 1.8
Upgrade JFrog build-info-extractor-gradle to 2.2.2
Move 'expandPlaceholders' to 'reference' ext

Move 'expandPlaceholders' into the 'reference' configuration rather
than relying on projects.ext.
Spaces -> Tabs
Add ability to configure fop-userconfig.xml.

With the ability to provide a user configuration of fop you can
add now new fonts to the pdf-renderer and build fancier output.
Merge pull request #19 from stephanheinze/master

* pull19:
  Add ability to configure fop-userconfig.xml.
Polish README
Style toc consistently regardless of <part/>

Update CSS to style TOC elements based on depth, rather than using
specific spans. Allows documents that do not include <part/> sections
to render correctly.

Issue: #16
Add sample showing transitive = false

Issue: #18
Release version 0.0.5