Fix cursor jump in form case management

[Ticket](http://manage.dimagi.com/default.asp?150383#838103)

If you started typing in the middle of any of the "Case Property" fields on the form "Case Management" tab, your cursor would jump to the end of the field. That was happening because the value of the field was manually being set after each change event, which resets the cursor position. The cursor position is now preserved by saving it, then reseting it after the text value is changed.

Note that this is achieved by adding a new library to the project: https://github.com/acdvorak/jquery.caret .