Bug 1094142 - Support DOMString/MozStkTextMessage for confirmMessage/callMessage in SET_UP_CALL/LAUNCH_BROWSER. r=frsela

Due to the icon support for SET_UP_CALL/LAUNCH_BROWSER to be done in Bug 1091454, we'd like to change the data type of confirmMessage/callMessage from DOMString to MozStkTextMessage, where MozStkTextMessage is defined a container for both text/icons.

Hence, this patch is required to prevent function broken after the patches of Bug 1091454 is landed.