Bug 104986 Backgound image uses an absolute path
Currently Chart uses an absolute path to indicate a backgournd image, that may cause the design unusable on other environments. Expected the background image can be definded in multiple ways like in report designer. e.g. URI(absolute path), File(relative path), Embedded Image(Encoded Image Data).
chart/org.eclipse.birt.chart.engine/src/org/eclipse/birt/chart/model/attribute/AttributePackage.java
EAttribute getSize_Height( );
	/**
	 * Returns the meta object for the attribute '{@link org.eclipse.birt.chart.model.attribute.Size#getWidth <em>Width</em>}'.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @return the meta object for the attribute '<em>Width</em>'.
	 * @see org.eclipse.birt.chart.model.attribute.Size#getWidth()
	 * @see #getSize()
	 * @generated
	 */
	EAttribute getSize_Width( );
	/**
	 * Returns the meta object for class '{@link org.eclipse.birt.chart.model.attribute.Style <em>Style</em>}'.
	 * <!-- begin-user-doc -->
	 * <!-- end-user-doc -->
	 * @return the meta object for class '<em>Style</em>'.
	 * @see org.eclipse.birt.chart.model.attribute.Style
	 * @generated
	 */
	EClass getStyle( );
	/**
	 * Returns the meta object for the containment reference '{@link org.eclipse.birt.chart.model.attribute.Style#getFont <em>Font</em>}'.
	 * <!-- begin-user-doc -->
	 * <!-- end-user-doc -->
	 * @return the meta object for the containment reference '<em>Font</em>'.
	 * @see org.eclipse.birt.chart.model.attribute.Style#getFont()
	 * @see #getStyle()
	 * @generated
	 */
	EReference getStyle_Font( );
	/**