Bug 151361 default value for reousrce folder user preference
When user does not sepecify the resourec foler user preference, can we make the current project folder (in IDE) or the current report design file's folder (in RCP) as the default value for the resource folder. This way, by default the current project folder is the resource folder where user can create their libs and images. Also please set the default user preference to be null when BIRT is freshly installed.
UI/org.eclipse.birt.report.designer.ui/src/org/eclipse/birt/report/designer/ui/ReportPlugin.java
*            elements - the Strings to be converted to the preference value
	 */
	public void setLibraryPreference( String[] elements )
	{
		StringBuffer buffer = new StringBuffer( );
		for ( int i = 0; i < elements.length; i++ )
		{
			buffer.append( elements[i] );
			buffer.append( PREFERENCE_DELIMITER );
		}
		getPreferenceStore( ).setValue( LIBRARY_PREFERENCE, buffer.toString( ) );
	}
	/**
	 * Return the library preference as an array of Strings.
	 * 
	 * @return String[] The array of strings of library preference
	 */
	public String[] getLibraryPreference( )
	{
		return convert( getPreferenceStore( ).getString( LIBRARY_PREFERENCE ) );
	}
	/**
	 * Set default library preference
	 */
	public void setDefaultLibraryPreference( )
	{
		getPreferenceStore( ).setDefault( LIBRARY_PREFERENCE, "" ); 
	}
	/**
	 * Return default library preference as an array of Strings.