[CB-3022] add default textbox value for notification.prompt

- document adding default textbox value parameter for notification.prompt
[CB-2598] remove iOS doc reference to navigator.fileMgr API

-remove iOS doc reference to non-existing navigator.fileMgr API
Merge branch 'master' of https://git-wip-us.apache.org/repos/asf/cordova-docs into CB3043