Bug 831737 Re-write and simplify newmailalert.{js|xul|css} (Backport changes from SeaMonkey Bug 404580) ui-r=paenglab r=mkmelin.

--HG--
rename : suite/mailnews/newmailalert.css => mailnews/base/content/newmailalert.css
rename : suite/mailnews/newmailalert.js => mailnews/base/content/newmailalert.js
rename : suite/mailnews/newmailalert.xul => mailnews/base/content/newmailalert.xul