Sort the result of scores_list_submitted

Signed-off-by: Stéphane Graber <stgraber@ubuntu.com>
Don't export None as a value of writeupid

Signed-off-by: Stéphane Graber <stgraber@ubuntu.com>
Rename writeupid to writeup_string

Signed-off-by: Stéphane Graber <stgraber@ubuntu.com>
doc: Document scores_list_submitted

Signed-off-by: Stéphane Graber <stgraber@ubuntu.com>