Traces can be added to and deleted from well log plots, and curves with
dummy data can be added and deleted. TODO: Replace dummy data with real
well log data and data extracted from the model.
Added command feature for adding new well log plots (right-click "Plots"
in the project tree view). Will create dummy Qwt widget added as an MDI
window.
TODO: Complete the relations between the entities, and add
properties/property editors. Create more advanced viewer widget for
plotting of multiple traces with multiple curves. Harmonize MDI stuff
with 3D viewers.
