Add type descriptor for module `dojo/i18n*`

[RoyTinker]

This adds a type dojo.I18nBundle and assigns that type to i18n bundles pulled in via dojo/i18n.

type I18nBundle = { [s: string]: string | I18nBundle };

When using it:

import i18n = require("dojo/i18n!./nls/Component");

//type of `i18n` is `dojo.I18nBundle`

[RoyTinker]

grunt test also fails on master with the same error.

[rorticus]

Ended up reverting this. After testing with the example apps, the recursive type makes it so this example,

@declare(DijitDialog)
class Dialog {
    title: string = messages.dialogTitle;
    content: string = messages.dialogContent;
}

had to be type-casted to,

@declare(DijitDialog)
class Dialog {
    title: string = messages.dialogTitle as string;
    content: string = messages.dialogContent as string;
}