Add portals to Neo4j database

[jmsevin]

• [x] Create hierarchical list of portals from Wikipedia FR
• [x] Generate dataset of article-portal associations from Wikipedia FR dump
• [x] Fill missing EN/ES translations for Level 1/2/3/4 portals
• [x] Generate 2D coordinates for portals (FR, EN and ES versions)
• [x] Add Portal nodes, Representation nodes and BELONGS_TO edges in Neo4j database