Added the ability to answer multi-values fields by an id

Example : A checkbox with choices Antelope, Zebra, Polar Bear, Kitten
Ids starts from 0, so if you want to check Antelope & Kitten your sms must
contains : 0,3
Available for checkboxes, radio buttons, and dropdown list

This feature is actually hard coded activated, I plan to completely change the settings part
of the plugin, the activation/desactivation of this feature will be included
Settings, modified

Integration of the settings page with Ushahidi plugin page
Added an option per new feature (already available or planned)
The settings page still needs some text for the user