Add support for web+ schema prefix

[Kubuxu]

As in chrome 'web+' is only allowed prefix for JS schema handling then most sites will be using it (and using JS to rewrite it to gateway). Accepting it and rewriting it to plain fs would be optional solution.

[lidel]

Yeah, the robustness principle is an important guideline for this add-on.
Due to Chrome's popularity it makes sense to accept yet another protocol variation and normalize it to canonical URIs.

[Kubuxu]

Same thing applies to transforming fs:, fs:// and fs:/// into fs:/.

[lidel]

Those are already supported.
(As of version 1.3.1 all custom protocol handlers redirect to URL of the custom HTTP gateway.)

[lidel]

Renamed the ticket as we should support chrome prefix for all handlers: web+fs:, web+ipfs: and web+ipns: (with / // or ///)

:)