Themes devguide

Besides the basic updates and corrections that were mentioned in the ticket, I added a new section in the predefined settings section for site maps. This consists of two new configurable settings that are similar to borders and bullet styles.

Also, I updated some content in the Developer Mode section. Because the wiki that this was based off of was created in 2008, properties and settings have changed.

https://issues.liferay.com/browse/LRDOCS-466