Closes #2602

Closes #2596

Closes #2601

Closes #2600

Adds undocumented/experimental “master issue” feature.

Setting `config.masterIssue = true` will result in Renovate opening and maintaining an issue that contains a list of all PRs both pending and open, and allowing some control over them (e.g. bypass schedule, force retry, etc).

Setting `config.masterIssueApproval` in addition will mean that branches are not created automatically and instead await approval in that master issue.

Closes #2595

Adds capability to upgrade major versions of Go Modules. Includes special handling for gopkg.in modules.

Closes #2583

Closes #2589

Adds support to update dependencies that have pseudo-versions like v0.0.0-20140422174119-9fd32a8b3d3d.