Generalized debouncing of translation API calls

[trevorparscal]

Hitting translation APIs too quickly can cause APIs to return errors in the short term and burns through quotas in the long term. Debouncing works great, but should be a lower-level feature of the base translation class.

[santhoshtr]

cxserver has a html reduce and expand feature that transform the content to a very minimal version to save quota(and security, bandwidth, workaround MT engine bugs etc) https://github.com/wikimedia/mediawiki-services-cxserver/blob/master/lib/lineardoc/Doc.js#L459