Con_Message(): Always append a terminating line break

Unlike Con_Printf() (which deals with text fragments), Con_Message()
assumes that (at least) one full line of text is being flushed.
Therefore the terminating '\n' character may be omitted from the
format-string argument.
Materials: Client-only decorations; Reworking manifest derivation

Material decorations are now rebuilt automatically following an
engine reset.

Material decorations now exist only on Client side. On Server side
the definitions are parsed as before however no Material::Decoration
will be instantiated.
Fix out-of-bounds memory access in Sfx_PurgeCache()

An oversight in the previous refactoring.
Cleanup