Support loading behaviors from a Git repo with branch + path

[ikreymer]

As a follow-up to #707, perhaps it'd be helpful to be able to specify a git repo, which the crawler would then clone locally.
Looks like we already have git installed in the image. The main addition would be how to specify the repo, for max flexibility.

Perhaps it could be: --customBehaviors git+https://git.example.com/repo.git@branch#root/path where the @branch and /root/path would be option.

Eg. given git+https://git.example.com.git@branch#!/root/path, the crawler would do:

git clone --branch branch https://git.example.com.git /tmp/behaviors-repo
cd /tmp/behaviors-repo
cd root/path

and then grab all of the behaviors from the current directory.

[tw4l]

Implemented branch and path as query parameters in the Git repo URL passed to the crawler in #717