Proper handling of git dependencies

[dmerejkowsky]

Right now we can edit the requirements.lock by hand to put a git url in it, but that's not ideal.

Ideas:

• Add a new command to automate the process
• Do some magic in the setup.py, like a git_dependencies keyword or something

[dmerejkowsky]

Other idea: https://stackoverflow.com/questions/32383640/why-does-setuptools-not-understand-githttps-urls

[dmerejkowsky]

In the mean time, we added a dmenv bump-in-lock command that automates the process in 0.7