Fix checkbox selection bug

-Checkboxes by people’s names would previously only be selected the
first time you clicked someone’s name.  If you clicked them again, the
checkbox would remain unselected.  (Provided of course that you didn’t
click the checkbox part of the name)
-Using jQuery prop instead of attr fixes this problem
-Reminified the friend-selector js as well
Merge pull request #16 from smilli/checkbox-fix

Fix checkbox selection bug