Fix Step infobrowser and examples localization

Summary: Currently (version 19.12), all object info and examples localizations are useless. This patch fixes current way of extracting and using Step translations.

Test Plan:
1. Extraction works. However, I'm uncertain if it is worth to have separate catalogs for object infos and examples (please, give an advice).

2. Translation (when put into the common /po dir) compiles and works. Translations are installed into the objinfo/<locale> dir to avoid conflicts with current lag packs. It is tested that Step can display the compiled localized HTML files.

Screenshot with translated tutorial and infobrowser (Ukrainian, clean install):
{F7773066}

Reviewers: #kde_edu, #localization, cordlandwehr

Reviewed By: cordlandwehr

Subscribers: ltoscano, pino, aacid, cordlandwehr, kde-edu

Tags: #kde_edu

Differential Revision: https://phabricator.kde.org/D25405