Updates to User Guide for version 0.4.0

This ticket is for making the following changes to the User Guide:

• Add a description of the flow.xml.gz to the Terminology section since we hadn't previously mentioned flow.xml.gz anywhere in the guide (yikes!)
• Add a "connection menu" section and image to the Connecting Components section so as to have a place to describe the new "Empty Queue" feature.
• Add a processor menu, process group menu, and remote process group menu description and image to the section on adding components to the flow.
• Fix a few typos.