Rather than manually parsing the output from the repo's host, the Addon Manager
now uses an embedded QWebEngineView to display the README data. This makes the
display more repo-location agnostic (rather than trying to parse the specific
code from GitHub, Gitlab, etc.). Special handling of known hosts is still
provided to improve the display of the page, but it is not required. Clicking a
link on the page still loads in a new system browser window, with the exception
of links to the FreeCAD wiki, which are loaded in the same browser. This is
expected to be used primarily to access traslated pages for Macros, so no
advanced web-browsing features are displayed (e.g. back buttons, history
access, etc.).
