Add support for pipenv as a manager. Disabled by default (needs opt-in) until out of beta.

Closes #2212

Closes #2850

New config option replaces existing option exposeEnv. Set trustLevel=high in the bot config if you trust the contents of the repositories you are renovating. Doing so results in env being exposed, access to localhost, etc.

Closes #2739

Closes #2806

Closes #2799 

Closes #2809

Closes #2785

.. and don’t create PRs.

Closes #2786

Begins #1870

Fixes #2771

Closes #2764

Support setting git clone protocol `http`, `https` or `ssh`.
Config name: `gitFsProtocol`.
Platform independent.

Closes #2708

Adds a call to getBranchStatus() from getPr() so that we are correctly calculating pr.canMerge status.

Closes #2735

In `getPrFiles` function, when requesting MR changes to GitLab API
(in order to return files modified by the MR), we should iterate over
`changes` property in the HTTP body response, and return `new_path` as
the filename.
See: https://docs.gitlab.com/ee/api/merge_requests.html#get-single-mr-changes

Closes #2748

This reverts commit ea8bcbc9.

This reverts commit 8f0279ec.