Closes #2302

Adds description if onboarding PR is edited or conflicted. Removes config description if PR has been edited. Adds description of PR rate limiting.

Closes #1317, Closes #1684, Closes #1359

De-dupplicates text in the onboarding PR and makes it closer to what the theoretical commit message would be.

Closes #1315, Closes #2211

Closes #2304

Fixes #2283, Fixes #2119

Closes #2299

Closes #2291

Pushes “getPrBody” logic into platform level to allow platforms to individually do things like text replacements and body length limiting.

Closes #2267

Adds new config option `rollbackPrs` which defaults to `true` (current behaviour). Setting to false will disable creation of rollback PRs - configurable globally, per-language, per-package, etc.

Adds support for .gitlabci.yml files. Part of the logic is same as Docker Compose files, however the “services” list is new/different so requires additional logic.

Closes #1598

"docker" in config now refers to the Docker "language", which is the parent of dockerfile, docker-compose and circleci managers.

This reverts commit 4ecbbc77.

chore: update node:8.11.3-alpine docker digest to deb628