Cherry pick our changes from master branch

Description

This mr cherry picks the changes from the master branch. As we are shifting to main branch as default which contains the latest changes from default as its a fresh branch therefore it doesn't contain the patches we did before. The changes are:

1. Disabling custom theme engine
2. Disable intro screen and changelog
3. Change url links from upstream to e gitlab
4. Integrate elib

Issues

e/backlog#1348 (closed)
e/backlog#1364 (closed)
e/backlog#4140 (closed)

10 commandments of code reviews

👪 ❤ https://gitlab.e.foundation/internal/wiki/-/wikis/development/code-review