Nightly builds

[mallocator]

Set up automation on Github to create a nightly build that runs against all integration targets.

Travis CI supports cron triggers and so this is likely to involve those. Maybe successful tasks will make a commit to a nightly branch that travis will trigger on.

Acceptance Criteria:

• All dependent projects should have a nightly build (e.g. Elasticsearch should run through all combination of version)
• Once dependent projects are successful the full bundle should run a test on all platforms (win, osx, linux)
• Tests should not run if there have been no commits since last build
• There should be a way to trigger a full build manually