Add support for SSH connections with private key authentication

[Nicklas Nordborg]

Implemented in BASE: ​http://base.thep.lu.se/ticket/2112

We need to update to BASE 3.13, remove BouncyCastle (​http://base.thep.lu.se/ticket/2111).

See also #1035, #1036 and #1037 which provides the same functionality for the OpenGrid Scheduler extension.

[Nicklas Nordborg]

(In [4751]) References #1038: Add support for SSH connections with private key authentication

Updated to use BASE 3.13 and removed BouncyCastle.

[Nicklas Nordborg]

(In [4752]) References #1038: Add support for SSH connections with private key authentication

Updated to SSHj 0.23.

[Nicklas Nordborg]

(In [4753]) References #1038: Add support for SSH connections with private key authentication

Implemented support for using private keys stored on the FileServer item.

[Nicklas Nordborg]

(In [4754]) References #1038: Add support for SSH connections with private key authentication

Fixed some compiler warnings.

[Nicklas Nordborg]

(In [4755]) References #1038: Add support for SSH connections with private key authentication

Need to check for a password OR a private key or we get an exception if a password is missing.