* Remove mention of no longer used IRC network
Channels exist on matrix, and on libera.chat now.
* Correctly match only files with .png extension
The current search would match files such as 'createpng'.
* Fix comparison in script
The result was always false, due to comparing a literal string instead of a variable.
* Use correct license files from upstream
Correct license files obtained from:
https://www.gnu.org/licenses/old-licenses/gpl-2.0.txt
https://www.gnu.org/licenses/gpl-3.0.txt
https://www.gnu.org/licenses/old-licenses/lgpl-2.1.txt
https://www.gnu.org/licenses/lgpl-3.0.txt
* Refresh several shell scripts
This fixes several shellcheck warnings, as well as makes the code more
robust and have consistent codestyle between all the files.
* Trim excess whitespace
