Relax content-type matching

[CaptainCodeman]

This relaxes the Content-Type header matching in the context.Bind method.

Angular 1.x sets the header to application/json;charset=utf-8 (note the lack of any space after the ;) so checking that the string application/json; charset=utf-8 starts with that header fails which prevents Angular $resource or $http etc... being used without extra client work.

I think the match should be the other way round - check if the header starts with simpler application/json string instead and ignore anything else.

I added the applicationJSON const because ApplicationJSON is used for other things as well. It's not a very good name and should probably be called ApplicationJSONPrefix or something similar but probably shouldn't be exported. I'm sure there is some official Content-Type parsing / matching rule somewhere though so we should probably follow that.

[vishr]

@CaptainCodeman: Let me think over it.