sectransp: allow cipher name to be specified

Add parser for CURLOPT_SSL_CIPHER_LIST option for Secure Transport (ST)
back-end. Similar to NSS and GSKit back-ends, new code parses string
value and configures ST library to use those ciphers for communication.
Create cipher spec data structure and initialize the array of specs with
cipher number, name, alias, and 'weak' flag.

Mark triple-DES ciphers as 'weak', and exclude them from the default
ciphers list.

Closes curl#6464