Merge the ConceptNet side of semantic space building from assoc-space

This code used to be in assoc_space.build_conceptnet. Now it lives
within conceptnet's code, and imports assoc_space. This depends on
assoc_space version 1.0, currently in a separate git branch.
add more rules for de_wiktionary to the Makefile
Makefile DB fix; WIP on building assoc-spaces in pieces
ignore 'data' in git, even when it's a symlink
More efficient conjunction queries
remove debugging, add py2-compatible izip
fix complex queries and test them