Fix and improve metadata file for Flatpak (#426)

* Fix and improve metadata file for Flatpak

- Remove bolding
- Fix APP ID typo
- Fix project license
- Add releases tags
- Migrate to metainfo from appdata
- Change screenshot and add dark screenshot
- Clarify metainfo license

Co-authored-by: Edgar <Edgar@AnotherFoxGuy.com>
Co-authored-by: Semisol <hi@semisol.dev>

help/CMakeLists.txt

@@ -52,7 +52,7 @@ if( NOT CMAKE_SYSTEM_NAME MATCHES "Darwin" )
       install( DIRECTORY "${dst}" OPTIONAL
                DESTINATION "${_DATADIR}/tenacity/help" )
       
-      install( FILES "${_SRCDIR}/tenacity.appdata.xml"
+      install( FILES "${_SRCDIR}/tenacity.metainfo.xml"
                DESTINATION "${_DATADIR}/metainfo" )
    endif()
 endif()