key_negotiation.php: rename sessionkey to conversationkey
PHP/android: add crypt_ini.php as initialization for encrypt and decrypt conversation info
RegisterActivity.java: encrypt key-value of client [1/2]
LoginActivity.java: encrypt key-value of client [2/2]
register.php: decrypt key-value of server [1/2]
login.php: decrypt key-value of server [2/2]
crypt_ini.php: rename sessionid_4_initialize to session_conversationkey