Fix query_var mistake and allow for new no-team login rules from Bitbucket

I put the query_var setup in the `activate` hook with the rewrite setup, but it should actually have been in the `init` hook. This fixes that. The plugin won't deploy without this fix.

Also, as of February 8th (I think), BitBucket will no longer allow users to login as their team. So if your node URL is https://bitbucket.org/<teamname>/<reponame>/get/master.zip, you would need to setup your plugin settings to login as the team, which will no longer be possible. This change uses the POST data's payload->repository->absolute_url property to build the node_url, so you can login as yourself and still access private team repos. There is also a fallback to the username/reponame URL scheme if that should be necessary for some reason.