Message Archive page doesn't load in Internet Explorer 11

[Fishbowler]

Following the implementation of the HTML message archive viewer in #35, I tested it in IE11 and found the page not to load.

Debug console shows this is due to the JS using fetch, unsupported in olde-worlde JS.

Even if fetch were supported, the subsequent promises wouldn't be - to become useful here, this needs to polyfill both, or rewrite to use neither.