Merge the -baseline and -additional tests for Selectors API level 1.
Remove the baseline/additional split from selectors.js.
Remove trailing whitespace.
Move the selectors-api tests to dom, where they now belong.
Remove trailing whitespace.
Replace tabs by spaces.
Merge pull request #1167 from Ms2ger/selectors

Cleanup the querySelector{,All} tests; r=MikeSmith+jgraham