Server plugin interface

• FTP, HTTP, SCP, SFTP and other remote connection protocols should use the same interface.
• new plugin type: Server.
• use the current connection details dialog with some improvements.
• add a button "Extended connection details" to the dialog. I imagine something like the "Configure" button in the pack files dialog. The button opens a dialog where extended connection details can be set.
• add a combobox "connection type" to the dialog. FTP is the default. If you have installed the "sftp server plugin" SFTP will be shown in the combobox and so on.
• If you have selected SFTP the "extended connection dialog" for SFTP will be shown after you pressed the "extended connection settings" button. This dialog is provided by the plugin (if necessary).
• Even FTP should have such a "extended connection details" dialog to offer an uniform interface to the user an to make the "connection dialog" more clearly (all FTP specific settings in the current dialog should be moved to the extended dialog). Of course FTP could be implemented as a plugin too, but that's not really important, because it's a Total Commander core feature.
• Some filesystem plugins have one more entries somewhere in the filelist to add and edit connections. (Smartbrowser) is a good example to see that filesystem is not the right kind of plugin for this.
• Quick connect should be supported by the new plugin interface.