Update function load_node_data in passive.py

Updated the load_node_data function in the passives.py module so that
the function now loads the contents of the file that contains the node
IDs, node names and descriptions/bonuses of all the nodes in the tree.
Add file create_skill_node_file.py

Added the file create_skill_node_file.py. This python module parses the
skilltree json file that comes with the offline skilltree calculator (it
is also available inline from the passive tree website code on the PoE
site). The module retrieves the node IDs, node names and
description/bonuses and outputs a csv file in tab-delimited format.
Use correct file to load skillnode info in passives.py

An incorrect filename was accidentally used in the function that loads
the skillnode info in the passives.py module. The name of the file has
been updated to reflect the actual name of the file.
Remove unused import json in passives.py

Removed an unused import of the json library in the passives.py module
to clean up code.
Add function get_bonus_for_selected_nodes to passives.py

The function get_bonus_for_selected_nodes was added to the passives.py
module. The function currently retrieves the names and description of
all the skilled nodes and prints this information to the console.

Later this function will return a dictionary that can be used to extract
the passive bonuses per type.