classic ui: Include more logos #4057

   This commit adds the file "Copyright.txt" in the "images"
directory and details the current statte of copyright and licensing
of the various images therein and in the "logos" hierarchy to the
best knowledge of the file's author.

   Credit is given to the individual who created the F*Nagios icon
set and who granted permission for the Icinga Project to redistribute
them freely.

refs: #4057
Merge branch 'feature/include-more-logos-4057' of git.icinga.org:icinga-core into feature/include-more-logos-4057