Modeling Commons bugfixes (issues 304 and 305)

Issue 304: Removed ability to resize upload dialog (one line fix in UploadDialog.java: this.setResizable(false) )

Issue 305: Fixed bug where login window persists after hitting cancel after having logged in and out.  Caused by missing else clause in onReturn method of LogoutRequest.java.

Additionally: 
Changed behavior when uploading models: when you click upload model and there is no connection, the user is sent back to the upload model dialog rather than shown an error dialog.  

Cleaned up for consistency error messages for bad connections and server errors