Tests sendwebpush

[gauntface]

This adds methods for testing sendWebPush in it's current state.

[gauntface]

cc @petele @wibblymat @addyosmani @jeffposnick

Anyone for a review?

[jeffposnick]

Might as well switch to 2016.

[jeffposnick]

Looks good in general. One piece of feedback with a scope that extends outside this PR is that it could be more maintainable to create a standalone file that included an enum-like mapping of error identifiers to error strings, and then refer to the errors via their identifier when constructing them in the library and when checking for them in the test.

[gauntface]

Ta for the review Jeff (The mocha exit with status 0 is super frustrating!!).

Raised an issue regarding the error message (agreed that this doesn't scale well or maintain well) #12

[gauntface]

@wibblymat when you get a chance, I'd appreciate you check over the code in push.js to make sure you are happy with them and I'm not missing anything.

[wibblymat]

Superceded by #18