First crack at SFTP support, and other stuff.

1. Fix LibMp3Lame calling convention to Cdecl.
2. Split out the Log class to its own file.
3. Split out utility methods from Program.cs to their own file.
4. Fix UI bug in ConfigControl causing SFTP fields to not become enabled
when checking the SFTP Enabled box.
5. Implement SftpUploader class as a thin wrapper around Renci
SftpClient.