Graph Based auto find master-tex feature

This improves the auto-find latex master feature by constructing a graph of inclusions: the algorithm would store for each file in the current directory which file includes which. Then it traverses the graph to find the first includer of the current file. One of the main advantages of this approach is that it correctly finds the latex master when there are more masters in the same directory as long as the current file is not included in more than one.