(1) Added a new "trend_line" variable to class "GraphParameters" and updated the function "generate_figure" in module "hydrograph" accordingly.
(2) Added a new "WLref" variable to class "GraphParameters". Parameter is not fully implemented in "hydrograph" module yet.
(3) Made "GraphParameters" class completely independent from the UI and moved it to "hydrograph" module. It is now possible to plot hydrograph outside of UI for testing and development purposes.