Adding X-Travis-Repo-Slug header to webhook requests

so that consuming the request body isn't necessary to calculate the
validity of the Authorization signature.
Allow to pass source to cancel services
Add source to cancel_job message in UpdateJob service
Escape commit message in build finished email
Clean up build event payload.

Exclude source_key, reinsert some commented-out tests, remove
stale code.
Merge pull request #268 from travis-ci/mm-fix-event-payload

Clean up build event payload.
Switching to a non-X header per rfc6648

plus removing rand in the spec per feedback from @henrikhodne.
notifications: Add build_id as a template variable

Closes travis-ci/travis-ci#1333.
Merge pull request #269 from travis-ci/hh-add-ids-to-notification-template

notifications: Add build_id as a template variable
Don't reset matrix state if all jobs are still running
Merge pull request #271 from Aaron1011/fix_state

Don't reset matrix state if all jobs are still running
Merge pull request #267 from modcloth/include-x-travis-repo-slug-header-for-webhooks

Adding Travis-Repo-Slug header to webhook requests
add services and api v2 for finding and deleting caches
remove obsolete file
remove obsolete line
make test timezone independent
Merge pull request #273 from travis-ci/rkh-caches

find and delete caches
do not raise exception if cache options are missing
Remove global_env_in_config feature flag

This flag was added in order to allow deploying a fix for allow_failures
and global env before we deploy corresponding changes to the workers.
It's no longer needed, because workers are already updated.
the workers table, and indexes, are no longer used