Implemented hummingbird.me and reworked code slightly to allow more flexibility for providers

Some sites, like hummingbird.me, rely heavily on javascript to deliver the anime list content making it impossible to get the content with a simple http request. Fortunately hummingbird.me has a JSON API which I made use of instead.

The major changes I made are:
* added `beforSend` function to anime-list-provider, called before sending anime list request
* added `overrideParse` function to allow custom/non-regex parsing of anime lists
* added `apiUrl` and `apiUrlSuffix` used only to retrieve anime list and not displayed to user in popup
* included `responseType` for anime list request (defaulting to `text`) for a consistency with `beforeSend`

Note: In the hummingbird provider I send a header with an API key I generated on [mashape](https://www.mashape.com/vikhyat/hummingbird-v1).

I recognize that this isn't a beautiful fix but I made it for myself and I figured I might as well share in case it can be of use to the main project. Perhaps a more complete reworking of the provider processing code is in order to better handle cases like these.