Implement new features for svg components + improve form properties (#25)

- Make Dimension an actual svg line
- Implement XPositionReference
- Select the container above after delete
- Remove DimensionLayer
- Improve form properties

Reviewed-on: https://git.siklos-chaneru.duckdns.org/Siklos/svg-layout-designer-react/pulls/25

src/utils/default.ts

@@ -36,3 +36,5 @@ export const DEFAULT_MAINCONTAINER_PROPS: Properties = {
   fillOpacity: 0,
   stroke: 'black'
 };
+
+export const NOTCHES_LENGTH = 4;