Changed class/id pattern for content sections

• Removed ‘fp-’ prefix from section IDs that are also used on
non-front-page pages.
• Switched composers ID to class to accommodate double block on
composers archive
• Switched CSS to use p-section vs fp-section as distinguishing page vs
front page
Added background images

Credit: http://subtlepatterns.com
Declared background image variables
Declared background styling for major sections
Applied background image to archive years list
Removed last margin from composer archive
Tweaked composer archive margin to 6px
Reduced bottom margin on more events link
Updated comments to match new ID/class scheme
Switched bg usage to avoid small-screen image load
Added overlay background to past composers list
Added external-link icon to colloquium map link
Added colloquiua location to foot of listings
Applied blurb styling to internal div not parent
Added page width restriction for biggest screens
Commented media queries
Increased composers third-level heading size

Matches headings elsewhere
Added overlay background to frontpage archive link
Reduced 2nd-level heading size for small screens
Added edit link to top of pages if user can edit