Roundcube webmail 1.1-beta

This is a beta release of the next major version 1.1 of Roundcube webmail.
With this milestone we introduce a bunch of new features and some clean-up
with the 3rd party libraries Roundcube uses:

• Allow searching across multiple folders
• Improved support for screen readers and assistive technology using
  WCAG 2.0 and WAI ARIA standards
• Support images in HTML signatures (copy & paste)
• Added namespace filter and folder searching in folder manager
• New config option to disable UI elements/actions
• Stronger password encryption using OpenSSL
• Support for the IMAP SPECIAL-USE extension
• Support for Oracle databases
• Moved 3rd party libs to vendor directory, managed by Composer

And of course plenty of small improvements and bug fixes.

IMPORTANT: with this version, we dropped support for PHP < 5.3.7 and
Internet Explorer < 9. IE7/IE8 support can be restored by enabling the
legacy_browser plugin.