Clean up after each test
Call attributeChangedCallback in `attachedCallback`

To make sure they are called before launching the gadget

Should fix https://github.com/Versal/versal.com/issues/2710
Inlined CSS so we don’t get a Karma error and to have one fewer request
Trying to fix Travis
Merge pull request #51 from Versal/fix-versal-com-2710

Fix Versal/versal.com#2710