Added background linting

Background hasChangedSignificantly is soon!
Merge pull request #885 from codecombat/master

Merge master into worker-lint
hasChangedSignificantly async refactor

Still checking for bugs
Fixed race condition
Added background transpile
Removed superfluous comment
Renamed test_worker to aether_worker
Removed web worker logging listener
Merge pull request #894 from codecombat/feature/worker-lint

Background linting/transpilation/hasChangedSignificantly