display default error message for non-json responses (TNL-5818)

[studio] log ajax errors. (TNL-5818)

[studio] fix failing test (TNL-5818)

[cms-test] avoid circular error logging; stub Logger (TNL-5818)

[cms-test] fix logger dep in squire config (TNL-5818)

[cms-tests] fix logger import (TNL-5818)

[cms-test] stub the logger directly in the karma config. (TNL-5818)

[studio] didn't need Logger after all (TNL-5818)

[studio] ignore console.log (TNL-5818)