Prepare documentation pages for automated translation

Qt documentation pages should mark snippets, class names ... as not translatable.

Motivation

Automated translation of webpages is becoming more and more popular. One can for instance translate a web page via Google Translate. Chrome supports this automatically by a 'translate' button.

Anyhow, when doing this for doc.qt.io, a couple of issues emerge:

• Code snippets like the qmake, CMake include lines for class information is partially translated too. For instance 'REQUIRED COMPONENTS' keywords in CMake become 'ERFODERLICHE COMPONENTEN'.
• Function names, types, and argument names are partially translated, too.
• Fixed names like 'Qt Core' or 'Qt Test' are translated, too

Proposed fixes

Code snippets, keywords ... should be marked with class="notranslate" in the generated html. This should be fairly easy to do as part of qdoc for fixed places. Anyhow, for module names etc we might have to enforce dedicated macros ...