remove failing and unnecessary jquery-ui require
update activeadmin dependency to allow newer versions
Allow for mounting as an engine

Sort URL generation should be irrespective of the app/engine url_helpers to allow for mounting as an engine- #url_to replaced with #resource_path

fixes #5, fixes #8, fixes #13
Merge branch 'master' of github.com:bespokepost/activeadmin-sortable into bespokepost-master
release 0.0.2