* [Installation] Updated the contents of the installation section.
[Code Cleanup] Minor edits
* [Worker Guide] Revamped the worker guide.  Improved the 'Logging in' page.  Completely rewrote the 'User Interface' introduction to fit on one page.  Updated the 'Preferences' page to cover the latest content.

* [Concepts] Moved the Concepts chapter from the beginning to the end, since it was too abstract for an introduction.