Uploader refactoring

- Changed IUploader into an abstract base class
- Keep the session alive instead of creator a new uploader every time
- Oh god I can't believe I still used #regions here
Remove WinSCP in favor of SshNet
Made `Manager.Uploader_get` less ugly as shit
Invalidate `Manager.uploader` when config changes
Remove WinSCPnet reference
Merge pull request #27 from horsedrowner/iuploader-session

Bye bye WinSCP