Please do some research on the following graph data structures related subjects; - "konigsberg bridge problem" and why it is important on graph data structures research. - Does "konigsberg bridge problem" has a solution? To have a solution, what should be added/removed from the problem? - Please explain each in the context of graph data structures: vertex, edge, degree of a graph, in-degree of a graph, out-degree of a graph, di-graph (directed graph), undirected graph - Please explain spanning tree of graphs and their types - Please search on graph based databases and their features and differences - Please explain Graph Based Neural Networks and their features.