Change the textual representation of fractional units to use Unicode superscripts...

Change the textual representation of fractional units to use Unicode superscripts and subscripts.  Unfortunately, the default fonts included with iText do not have these characters mapped so we needed to switch to a new true type font DejaVu.  Added the DejaVuSerif font definition to the resources and modified the pdf writing process to use this font.  Because this font is slightly wider, the column headings in the DesignReport had to be made smaller.  Finally, had to modify the ExpressionParser to convert the unicode chars to real digits in order to have the expression parser be able to work with this representation.

git-svn-id: https://openrocket.svn.sourceforge.net/svnroot/openrocket/trunk@704 180e2498-e6e9-4542-8430-84ac67f01cd8