Add install package at new project stage

[gshotwell]

I use a distinct venv for each project, but I often find myself installing the same packages when I get started. It might be nice to allow the user to select packages they'd like to install when creating a new virtual environment project, this could remember the packages that you selected last time or refer to a user setting.

[juliasilge]

We have #1529 where we talk about letting folks use, say, a requirements.txt plus a Python version as a template for new projects. This is an interesting related idea!