Fix the order of HtmlImports/CustomElements and the event in the test

Note that before this our tests failed in Chrome 36, as it doesn’t fire HTMLImportsLoaded anymore
Use newest versions of dependencies

Most importantly:
HTMLImports: 0d3133d19b
CustomElements: 65bb151f33
MutationObservers: a8aa7f9cc3
WeakMap: 6662df5cb7
Merge pull request #10 from Versal/fix-dependency-order

Fix dependency order