Closes #2752

Adds support to run Renovate like “renovate owner/repo —dry-run”. Instead of creating branches, PRs or comments, an INFO level dry run message will be logged each time instead.

Closes #1399

Closes #442 

Include body, message and stack with every error if present

Fixes #2283, Fixes #2119

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

Closes #2267

Closes #2141

Closes #2101 #2092

This PR adds the feature of commenting on a failed automerge. It's done by adding a conditional in `lib/workers/branch/automerge.js` which, in case of receiving `failure` or `error` from the `getBranchStatus` function, returns the "branch status error" value. Another modification is in `lib/workers/branch/index.js`, which is an adition to the failure response of the `tryBranchAutomerge` function. The added functionality is the ability to add a comment to the PR which had a failure automerging. In case of receiving the aforementioned "branch status error" value, to the comment is appended a note which emphasize the fact that there're multiple failed status checks.

Closes #1934 

Renames currentVersion to currentValue, newVersion to newValue, newVersionMajor to newMajor, and newVersionMinor to newMinor.