Hardened TLS cipher suites and versions

As Georg Lukas wrote in his blog post about how Android handles TLS handshake (http://op-co.de/blog/posts/android_ssl_downgrade/), an explicit order of cipher suites and TLS versions must be supplied to
avoid having the weak (presumably broken) RC4 cipher at the top of the preference list.

This commit adds the list included in the blog post to every TLS socket creation, including IMAP, POP3 and SMTP, see Wireshark screenshots done during testing at http://vsza.hu/k9mail-tls-hardening/