Change accelerators for section navigation

The accelerator keys for navigating the sections when not displaying
the whole source code conflicted with the well-known Ctrl+Right and
Ctrl+Left shortcuts for jumping to the next or previous word. Changed
to period and comma (i.e. same keys as < and >) as per the OS X front
end. Thanks to Jacqueline Ashwell for the suggestion.
Bring authors and credits up to date
Update Chimara and Osxcart

Chimara now needs to track the 'gtk2' branch, since master has updated
to GTK 3.