Now adding correct swt.jar to generated .classpath and small improvements.

+ Add correct swt.jar to .classpath depending on platform and architecture.
* Reformatted mix of tabs and spaces into spaces.
* Changed version of referenced swt-linux jar to be the same across the project.
+ Added "Kettle Extra" user lib to be included into generated .classpath files. The lib may be set up in IDE if needed and contain custom jars like JDBC drivers/etc.