Fix for bug #4547

Sometime back 'Add user' and 'Edit privileges' functionalities were Ajaxified and they used a jQuery dialog to display the relevant forms. However, due to the lack of space in jQuery dialogs, those functonalities needed to be reverted. This was temporarily done by directing the content which earlier went into the jQuery dialogs to a div above #page_content div. This wasn't the cleanest approach and it also broke the micro history. In this PR I am proposing to fix this and revert the ajaxification altogether, hence big deletions in js/server_privileges.js