Build Bacon with Rollup from ES6 modules (2.0 branch)

[raimohanska]

Same as #707 but merged onto the 2.0 branch

[raimohanska]

Needs fix:

• Current dist/Bacon.js doesn't work in browsers as-is: ReferenceError: global is not defined

Optional improvements that are not blockers in my opinion:

• Testing custom builds is broken. It used to be so that you can say test map and you'll get a build that only contains map and then tests for map are run. I don't see this as a blocker though.
• Get rid of grunt, build, test and run-tests scripts, use package.json scripts instead
• Move all scripts that are still necessary under scripts directory to cleanup the root

[raimohanska]

Fixed the global is not defined problem.

[raimohanska]

Current status:

• Testing custom builds is broken. It used to be so that you can say test map and you'll get a build that only contains map and then tests for map are run. I don't see this as a blocker though.