Specify loading the external dictionary

[Yoric]

We don't want the VM to need to download stuff, so this has to be done externally, i.e. by DOM.

[dominiccooney]

In addition to specifying actual fetches, etc. we probably need a preload type for these resources so browsers can start the dictionary and first BinAST fetch in parallel.

[sendilkumarn]

I think adding a preload is the best way to download the dictionary
But does that mean that each script tag (if there are multiple) would require this attribute and make vm intelligent enough to handle this?

[Yoric]

A few precisions after discussing with Annevk:

• we don't want same origin policy for dictionaries, as this would prevent us from putting dictionaries on a cdn;
• we want CORS, as all new features pretty much require CORS.

[Yoric]

I agree that a preload would be nice, but I believe that this should be a HTTP header, which could be returned either with the webpage itself or with the .binjs. This will make it easier for proxies to inject such preloads.

@RReverser, if you're around, what do you think about that?