Add configurable limit for action.share plugin

With this patch you can set a maximum time and
maximum download time for every new file share

Signed-off-by: Etienne CHAMPETIER <etienne.champetier@fiducial.net>
Use plugin Id instead of Name in class.ShareCenter.js
ajxp_plugin[@name='share'] -> ajxp_plugin[@id='action.share']

Signed-off-by: Etienne CHAMPETIER <etienne.champetier@fiducial.net>
Merge pull request #242 from echampet/sharelimits

Add configurable limit for action.share plugin
Fix groups when creating user from inside subgroup (fix #269)