mail-client/roundcube: Version bump, security, and bug fixes

mail-client/roundcube: Version bump, security, and bug fixes

Added two use flags controlling optional dependencies to support the
enigma and and sieverules plugins.

Added REQUIRED_USE as one of postgres, mysql, or sqlite must be
enabled. Rouncube requires a database to operate. As the ebuild uses
this now, removed the default enable on the mysql USE flag.

Added POST-UPGRADE.txt which is just a shortened version of the
UPGRADE text from upstream.

Dropped arm and ppc64 keywords as one dependency,
dev-php/PEAR-Net_LDAP2, currently lacks matching keywords for those
architectures.

Bug: 541172, 545096, 524192, 564476, 565204, 53284

Package-Manager: portage-2.2.20.1