Fluid 5439: Add docs for "Tutorial - Creating a New Adjuster UI" and panels in prefs framework.

@acheetham, this pull request is to replace the previous one (https://github.com/fluid-project/infusion-docs/pull/14) in order to get rid of the trace of binary image files from the commit history. Those image files were added for "font icon research" page that we have decided not to convert.

This pull request has addressed all your comments for the previous pull: https://github.com/fluid-project/infusion-docs/pull/14

Ready for another review.
This isn't really rendering nicely: It renders as one long line that needs horizontal scrolling. I like the box, but maybe "pre" is not the way to go. Perhaps all italics, with bold+italic for the header? Or at least, if we use "pre", add some line breaks so the reader doesn't have to scroll.