Dropped data files from POTFILES.skip files. Added missing source files to them.

Requested by Jacob Nevins <jtn>

See patch #4454


git-svn-id: svn://svn.gna.org/svn/freeciv/trunk@24330 a0f10bec-cc02-0410-94fc-a9cfff90b4cd
Allocate sdl2-client Main.gui

See patch #4419


git-svn-id: svn://svn.gna.org/svn/freeciv/trunk@24332 a0f10bec-cc02-0410-94fc-a9cfff90b4cd