Fix errors when using localStorage in Safari's private browsing mode (#1489996)

Conflicts:

	program/js/app.js
Set 'compose_extwin' env property on every step; accept a list of URL parameters for the 'compose' command
Fix missing css/js scripts in filter form in mail task

Conflicts:

	plugins/managesieve/Changelog
Fix bug where $Forwarded flag was being set even if server didn't support it (#1490000)
Merge branch 'release-1.0' of https://github.com/roundcube/roundcubemail into release-1.0