BiGCaT updates

• keyword fix: sib-swiss#24
  • example: https://bigcat-um.github.io/sparql-examples/examples/WikiPathways/004.html
• license + contributor support: sib-swiss#25
  • contributor example: https://bigcat-um.github.io/sparql-examples/examples/AOPWiki/000.html
• variable support: sib-swiss#26