Added Diffie Hellman Group 14 Key Exchange

Added support for SSH2 servers that don't support DH1.
Separated out generic DH code from DH1.pm to DH.pm and added
DH14 in DH14.pm
This will make adding different Diffie Hellman Groups
possible and easy with DH.pm as the base class.

Also fixed some indentation errors and added
StrictHostKeyChecking from Net::SSH::Perl v1.37 on CPAN