add water quality to the section plot

[jkall]

Parameter values are to be plotted with selectable symbols (default non-filled circle) of varying sizes with respect to min and max values in the data set. (Option: user are allowed to set min and max sizes). And data labels. Parameter values should be plotted at sampling depth (see below).

gui ideas.

A new tab in left pane with these filters-: Table: w_qual_lab or ..._field Parameter: Unit: Date: (first obs as with w_levels profile) Depth: editable list with obsid-depth. From start the list should be prepared with depth from the w_qual... table or, if missing in w_qual_table, from length in obs_points table.

On first (original) tab in left pane, or preferrably in the bottom and non-tabbed area, , the user can select to activate/deactivate water quality plot. Same way as today with stratigraphy and labels.

[HenrikSpa]

The gui update in branch simon-merge makes this addition much easier to accomplish.