Resolve "Add CentOS7 and CentOS8 pipelines to merge request"

To make code reviewing easier:

There are not so many actual changes - majority of them is just moving files, due to restructuring of build process and formatting them by clang.

Actual significant changes are in files:
.gitlab-ci.yml
.gitlab-ci-nicadist.yml
and directories:
gconfig
macro/mpd
macros/common

DO NOT REMOVE THIS BOXED MESSAGE

Code in this merge request is subject to review by Code Owners.
The list of reviewers is posted in the comments section.
After all of the code is approved, please put a brief notice about it at the beginning of this message.

NOTE: Merging this code without getting it approved by Code Owners will result in suspending your developer rights!!!

Closes #42 (closed)