Pull request quality assurance

When checking if PR could be merged or not the following criteria should be considered among others:

There should be either an issue linked to PR or PR should have a good description on what is it fixing or adding.
Unit tests. Not mandatory but very appreciated. These should fail without the code that the PR is fixing.
CHANGELOG entry should present. It should be put into next release section, ordered by issue type and number. Nicknames of people responsible should present.
Code style and views code style should be OK. These could be fixed while merging if the person merging prefers it that way.