Fix maven warnings, move JDK version and google api versions to properti...

...es, add enforcer plugin configuration

```bash
$ mvn package
[INFO] Scanning for projects...
[WARNING] 
[WARNING] Some problems were encountered while building the effective model for com.google.apis:google-api-services-genomics:jar:v1-rev20130925-1.18.0-rc-SNAPSHOT
[WARNING] 'build.plugins.plugin.version' for org.apache.maven.plugins:maven-jar-plugin is missing. @ line 76, column 15
[WARNING] 
[WARNING] It is highly recommended to fix these problems because they threaten the stability of your build.
[WARNING] 
[WARNING] For this reason, future Maven versions might no longer support building such malformed projects.
[WARNING] 
```

The javadoc configuration could also be improved.  E.g. I'm not sure if these are supposed to be resolvable

```
[INFO] --- maven-javadoc-plugin:2.7:javadoc (default-cli) @ google-api-services-genomics ---
[ERROR] Error fetching link: http://javadoc.google-http-java-client.googlecode.com/hg/1.18.0-rc-SNAPSHOT/package-list. Ignored it.
[ERROR] Error fetching link: http://javadoc.google-oauth-java-client.googlecode.com/hg/1.18.0-rc-SNAPSHOT/package-list. Ignored it.
[ERROR] Error fetching link: http://javadoc.google-api-java-client.googlecode.com/hg/1.18.0-rc-SNAPSHOT/package-list. Ignored it.
```
If they are, the version could be moved to a property value.  The version for maven-javadoc-plugin could also be bumped up to the most recent 2.9.1.