Key authentication with password

[ahitrin]

At the current moment, we could use passwordless RSA or DSA keys for authentication instead of password. Keys are taken from the default SSH key directory.

But passwordless authentication doesn't have good security level. In order to improve it, we should provide ability to set key password.

There are at least two implementation options possible:

• store password in accounts file (using reserved parameters rsaPassword and dsaPassword)
• ask user for password when xe tries to connect to account