Add support for Server Name Indication (SSL protocol extension)

[AutoImport-xylo]

Many private servers host multiple domains with different ssl certificates. In order to be able to use davdroid with those servers needs davdroid needs to implement the Server Name Indication instead of the classical SSL protocol: http://wiki.apache.org/httpd/NameBasedSSLVHostsWithSNI

[rfc2822]

Dup of #9