Add gradle-info metadata to pom files

Add a new plugin (nebula-metadata) that will pull data from gradle-info and insert the key/value pairs into the published pom file's <properties/> node.  The key's are prefixed with 'nebula.' to avoid collision and confusion with an existing properties.

The particular implement is the simplest path, but also likely the least desirable.  It results in a pom file that has a bunch of properties that may look foreign to somebody accustomed to maven pom's.  An alternative approach would be to add a new namespace (assuming that is possible) to the pom.xml.

Here's an example of the resulting pom file.
```
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <modelVersion>4.0.0</modelVersion>
  <groupId>nebula.hello</groupId>
  <artifactId>world</artifactId>
  <version>1.0</version>
  <dependencies>
    <dependency>
      <groupId>asm</groupId>
      <artifactId>asm</artifactId>
      <version>3.1</version>
      <scope>runtime</scope>
    </dependency>
  </dependencies>
  <properties>
    <nebula.Manifest-Version>1.0</nebula.Manifest-Version>
    <nebula.Implementation-Title>nebula.hello#world;1.0</nebula.Implementation-Title>
    <nebula.Implementation-Version>1.0</nebula.Implementation-Version>
    <nebula.Built-Status>integration</nebula.Built-Status>
    <nebula.Built-By>mmcgarr</nebula.Built-By>
    <nebula.Build-Date>2014-07-03_15:33:43</nebula.Build-Date>
    <nebula.Gradle-Version>1.12-20140608201532+0000</nebula.Gradle-Version>
    <nebula.Module-Source>/build/test/nebula.plugin.responsible.NebulaMetadataPluginLauncherSpec/published-pom-contains-a-collected-property</nebula.Module-Source>
    <nebula.Module-Origin>git@github.com:nebula-plugins/nebula-project-plugin.git</nebula.Module-Origin>
    <nebula.Change>0ab9baf</nebula.Change>
    <nebula.Build-Host>localhost</nebula.Build-Host>
    <nebula.Build-Job>LOCAL</nebula.Build-Job>
    <nebula.Build-Number>LOCAL</nebula.Build-Number>
    <nebula.Build-Id>LOCAL</nebula.Build-Id>
    <nebula.Created-By>1.7.0_51-b13 (Oracle Corporation)</nebula.Created-By>
    <nebula.Build-Java-Version>1.7.0_51</nebula.Build-Java-Version>
    <nebula.X-Compile-Target-JDK>1.7</nebula.X-Compile-Target-JDK>
    <nebula.X-Compile-Source-JDK>1.7</nebula.X-Compile-Source-JDK>
  </properties>
</project>
```
This kind of error should live in the buildManifest call, though that call is used in a few places (like the @Input on the Apply Manifest task), but the point is that it's core to the InfoPlugin, not a maven specific block of code.