Fetcher: Add demo mode

Usage: Run runner with 1st argument "demo" and path to .csv file of demo movies as second argument
   bundle exec ruby bin/tmdb_fetcher_runner.rb demo /path/to/movie_links.csv
Merge remote-tracking branch 'origin/master'

* origin/master:
  implemented function 'merge_into_entity'
  some fixes in mapper
  refactored sparql query; is working now
  added functions 'get_subjects_for' and 'get_predicates_and_objects_for' for merger
  merger uses general classes now; prov information is updated
  bug fix
  assigned functions in merger to Kerstin
  bug fixes
  DBpediaCrawler: implemented test run (see README)
  DBpediaCrawler: adjusted README :)
  DBpediaCrawler: using 'schema.org' instead of 'schema.rdfs.org' for adding types to fetched entities
  parse dates correctly