Merge pull request #10 from gvwilson/master

Adding miscellaneous links (and updating PNAS cover letter)
Merge pull request #15 from gvwilson/master

Adding and updating files
120 x 120 version of logo

New 120 x 120 px PNG version of the hammer-and-nail logo.
Reorganized admin folder to create branding subfolder for images, stylesheet

Created branding folder; moved logo files to branding folder. Created
stylesheet file. (This is probably too much for one commit...)
Merging