removed the Event model, table, and related services and api payloads

this was not used and will instead be replaced by a Request specific API endpoint
removed the Worker model and related services and payloads

also updated the schema from when the Workers table was removed.
Merge pull request #288 from travis-ci/jk_remove_worker_model

Remove the Worker model and related services and payloads
Merge pull request #286 from Aaron1011/fast_finish

Add support for fast_finish
gh gem moved to travis-ci/gh
remove the section in the readme on metrics
Merge branch 'master' of https://github.com/travis-ci/travis-core
Merge pull request #287 from travis-ci/jk_remove_event_model

Remove the Event model, table, and related services and api payloads
Allow to cancel on pull permission
Change default recipients list for builds

New rules:

1. If the build happens on the default branch, all members of the
repository are notified.
2. If the build is not on the default branch, the author and the
committer who are also members of the repository are notified.
Rework email event handler specs

Stubs are re-examined and fixed.
Add enough stubs to instruments spec
Remove unnecessary stub
Tweak how we determine build status

Build's config can have key-value pair `:matrix => nil` under some
circumstances.

If this happens, `[]` will throw a NoMethodError. We need to protect
ourselves.

Ideally, we want to write

```
matrix = Hash(config.fetch(:matrix, {}))
if matrix[:fast_finish]
⋮
```

but `Kernel.Hash` is not available in 1.9.3.
Merge pull request #294 from travis-ci/ha-bug-job_wait_status

Handle the case where config has `matrix: nil`.
Merge pull request #290 from travis-ci/ps-allow-to-cancel-on-pull-permissions

Allow to cancel on pull permission
Fix issue with fast-finish build matrix not passing.

Related to travis-ci/travis-ci#1688. This change also cleans up
the tests, which had the wrong expectations before and are now
actively testing for the fast_finish feature and the correct
return values.
Merge pull request #295 from travis-ci/mm-fast-finish-with-successful-jobs

Fix issue with fast-finish build matrix not passing.
Merge pull request #291 from BanzaiMan/core_gh94_email_notification_revamp

Change default recipients list for builds
Restrict def email notification to committer and author

Regardless of the branch, email only the committer and author of the
commit.
See
https://github.com/travis-ci/travis-ci/issues/488#issuecomment-29527429
and ensuing discussion on the rationale.