Some fixes and improvements

[sbrdar]

Description

• a fix to empty or missing atlas-tag causing crash in -make serve-
• fix version check for doxygen
• improve make help and notify of a missing Ghostscript
• make loading of libgs automatic

Contributor Declaration

By opening this pull request, I affirm the following:

• All authors agree to the Contributor License Agreement.
• The code follows the project's coding standards.
• I have performed self-review and added comments where needed.
• I have added or updated tests to verify that my changes are effective and functional.
• I have run all existing tests and confirmed they pass.

[wdeconinck]

Thanks for this @sbrdar !