meaningful node naming when using from_list()

[matjobst]

Implementation for Issue #20
This should not break any end user code because it is just a modification on the naming of the nodes generated by NIRGraph.from_list().
Naming follows Tensorflow convention:
First occurence of Node type will get classname in lower case, from the second occurence a _<i> is appended, where <i> is the count of previous occurences.
Example:
input -> dense -> dense_1 -> affine -> dense_2 -> affine ->output

[Jegp]

There are a few print statements that should be removed. And I had fun trying to find other ways to find a unique_node_name with some Python collection types.

Otherwise, nice addition :)

[matjobst]

Nicely spotted on the prints. They are removed now.
And thank you for the hint on the collections, I always forget about these. I implemented the Counter version now because it shows the intent of the code best.

[Jegp]

Nice! I like your way to do the format string with f"{}{}" it looks much better than f"{}" + ... :)