Fix #5.
Nested sandboxes reuse `oasisURL` as default.

This is convenient for the common case that `oasisURL` needs to be defined
exactly once.

Nested sandboxes can still define their own default by setting
`Oasis.config.oasisURL` or create sandboxes with a specific URL.
Increase testTimeout for Saucelabs
Remove Saucelabs' browser matrix widget

It doesn't currently support per branch image
Handle promise errors.

Fix #18.
Add support for IE8.

es5 → es3 via shims.
Hide passed tests by default.

Even in IE8.
Vain attempt to correct build.