ui: disable browser caching for front-end

[norwnd]

I've noticed when I have Bison wallet running, close browser and re-open it again - UI shows some stale data (especially noticeable on /markets page),

specifically I observe this with Chrome (Firefox for example handles it better somehow looks like),

the reason seems to be browser(s) use all sorts of caching - and in our case, browser doesn't reload the whole page but rather it sends some select requests to back-end (opens WS connection, requests maxbuy/maxsell and that's pretty much it),

this change seems to resolve it.