VectorVisualization: Added backwards compatibility for loading sessions prior to 1.11

With the added streambarbs, some session configurations were introduced. Previously, all settings were in the sub menu Windbarbs. With the added streambarbs, an additional sub menu Streambarbs got introduced. Some of the settings between the two visualization methods are shared: The variables for the u/v components, and information about the rotation/projection of the grid. With the streambarbs update, these settings were moved to the shared super level menu.

However, this made old session files incompatible. This MR adds a backward compatibility check that reads the settings from old session files correctly.