Report version of bwscanners in votes

Each directory authority should list the git version of the bandwidth scanners in their votes. This ticket has two parts:

1. Edit aggregate.py to output a line with the git commit that it is from.

2. Alter the tor voting to add an "opt" line or other ignored keyword that lists the version from the bwscan file.

There should be no consensus process for this. We just want a comment in the vote documents, basically.