Show #studies / #participants in network graph

[gertvv]

Thanks to Binod Neupane:

Network graph using plot.network function: The way gemtc produces graphs is great. But, I am not sure if there is an option to obtain more informative graph, ie, displaying the connecting lines widths thicker or thinner depending on the number of trials included in the direct comparisons; similarly bigger or smaller circle for each included treatment ( depending on the number of times tested); and writing down treatment name at the side.

[gertvv]

Number of studies per comparison was added to the network plot in 0.6-2.

Scaling of vertices is to be added later.