Improve translation web services performance by doing queries in parallel

Introduces QueryAggregator which uses MultiHttpClient class from core (1.23+)
and some necessary refactorings to be able to use it. As an added bonus,
web services classes now have less boilerplate http code, do not deal with
http directly and request creation is separated from response parsing.

The try-random-language loop, executed when the source language is not supported,
is now moved to MachineTranslationAid, as it does not make sense for
RemoteTTMServerWebService.

Removed copyright annotations as I am too lazy to keep them up to date;
anyone interested can look at the git history for more accurate information.

Bug: T88431
Change-Id: Id4f1c988f568cfb695f2b33c3dacdeed4aeafe6f