Remove the old gradient test suite, and replace by the modern one

The "gradients" test suite was built before gradients reach their final
syntax, and only checked them with a prefixed syntax. The
"unprefixed-gradients" is a rework of it, updating to the final syntax
as specified per the w3c, and supports the unprefixed syntax. Opera
needed to keep both for historical reasons, but only the later is
relevant to the rest of the world.
Remove time element test that has been submitted.

Submitted in https://github.com/w3c/web-platform-tests/pull/31.
Remove DOM XPath tests that have been submitted.

Submitted in https://github.com/w3c/web-platform-tests/pull/449.
Remove Microdata test that has been submitted.
Remove idlharness tests that duplicate existing tests.

* The idlharness tests are a subset of html/dom/interfaces.html.
* The 'x in document.createElement(script)' tests don't do anything, and
  would duplicate the idlharness test if they did.
* The initial value of script.async is tested in
  html/semantics/scripting-1/the-script-element/async_001.htm.
* The initial value of script.defer is tested in
  html/dom/reflection-misc.html.
Create LICENSE.txt
Add README for opjsunit
Merge pull request #11 from gsnedders/opjsunit-readme

Add README for opjsunit
Those tests are duplicated from the Web Performance Working Group and have been integrated in web-platform-tests
Copy info about opjsunit from internal dev wiki

Including some that is probably out of date
Removing Mozilla tests

Other vendors' tests were not intended to be part of this release
Merge pull request #5 from frivoal/gradients

Remove the old gradient test suite, and replace by the modern one
Merge pull request #6 from Ms2ger/timeelement

Remove time element test that has been submitted.
Merge pull request #7 from Ms2ger/dom-xpath

Remove DOM XPath tests that have been submitted.
Merge pull request #8 from Ms2ger/microdata

Remove Microdata test that has been submitted.
Merge pull request #9 from Ms2ger/idlharness

Remove idlharness tests that duplicate existing tests.
Merge pull request #12 from plehegar/master

Remove webperf specs and tests