gui: Settings dialog improvements and small logic change

!!! The real directory for the folder is now composed <PATH>/<shared-folder-name> !!!

In initial stage when there are no settings:
+ if FileDialog aborted, selected $HOME/ChronoShare as a base directory
+ if invalid folder specified, ask question again until aborted to valid
folder selected

At later stages:
+ if aborted, just exit
+ if the same folder selected, just exit
+ if invalid folder selected, ask again until valid folder selected or aborted
+ if different valid folder is selected, restart FsWatcher and Dispatcher for new location

For either stage:
+ if username or folder name not specified, don't hide/save settings.
Keep it until something is specified
+ if username or folder name changed, restart FsWatcher and Dispatcher
with new parameters

Change-Id: I19c34cb91f7375f88347542abe30b85a1c5d6d3f
diff --git a/gui/chronosharegui.h b/gui/chronosharegui.h
index fffaca7..c56baa5 100644
--- a/gui/chronosharegui.h
+++ b/gui/chronosharegui.h
@@ -112,9 +112,9 @@
   // capture close event
   void closeEvent(QCloseEvent* event);
 
-  // starts fs watcher and dispatcher
+  // starts/restarts fs watcher and dispatcher
   void
-  startBackend();
+  startBackend(bool restart=false);
 
 private:
   QSystemTrayIcon* m_trayIcon; // tray icon