D3graph

* Bug fix for nodes not showing up
* Bug fix that functions vec2adjmat and adjmat2vec could not be located
* Some code cleaning and refactoring

* remove of special chars in columns
* Fixed future pandas warnings
* Some code cleaning

Convert to adjacency matrix
adjmat = vec2adjmat(source, target, weight=weight)

Initialize with default parameters
d3 = d3graph()

Proces adjmat
d3.graph(adjmat)

Set node properties using the set_node_properties functionality
d3.set_node_properties(color=adjmat.columns.values)
Plot
d3.show()

Simply make changes in the node properties and plot again with d3.show()
print(d3.node_properties)

Simply make changes in the edge properties and plot again d3.show()
print(d3.edge_properties)

* Reduced complexity in the packaging by removing utils directory

* Freeze jinja2 at version 2.11.3 because version 3 and higher throws an error: https://github.com/pallets/jinja/issues/1168

added missing file to manifest