Github topics addition to the augur schema

[cdolfi]

Projects more and mroe are using the self identified github topics feature:

Topics are the ones in the blue circle
Link to topics overall: https://github.com/topics

It would be incredibly helpful to have this information a part of Augur.

Note: there is a bit of name collision happening as in the "repo_info" table there is a "topic_words" column. I was a little confused initially as I thought that was what that column data was.