developers-catalog.xml

The `catalog.xml` supplied with the Getting Started guide is good when using the Brooklyn distribution, but of limited value if building Brooklyn from source.

This `developers-catalog.xml` uses local `file://~/.m2/repository/io/brooklyn/...` classpaths, avoiding the need to pull artifacts from Maven/Sonatype while developing.

I added this catalog and a note to the `/dev/build/` part of the docs.

Also, note the *image* - **icon** . *format* image urls, now available on http://downloads.cloudsoftcorp.com.

http://downloads.cloudsoftcorp.com/brooklyn/catalog/logos/JBoss_by_Red_Hat-icon.png
![icon](http://downloads.cloudsoftcorp.com/brooklyn/catalog/logos/JBoss_by_Red_Hat-icon.png)

http://downloads.cloudsoftcorp.com/brooklyn/catalog/logos/JBoss_by_Red_Hat.png
![fullsize](http://downloads.cloudsoftcorp.com/brooklyn/catalog/logos/JBoss_by_Red_Hat.png)