Simplified the loading image from URL message to make use of existing dialog box types and text strings

git-svn-id: http://svg-edit.googlecode.com/svn/trunk@2512 eee81c28-f429-11dd-99c0-75d572ba1ddd
Two more loading messages for Import and Open of images.

git-svn-id: http://svg-edit.googlecode.com/svn/trunk@2513 eee81c28-f429-11dd-99c0-75d572ba1ddd