Include string.h in mPresentation.c to declare strcpy()

[olebole]

Otherwise, one gets the error (with gcc-14)

gcc -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64 -g -O2 -I. -I../../Montage -I../../lib/include  -c  mPresentation.c
mPresentation.c: In function ‘main’:
mPresentation.c:54:4: error: implicit declaration of function ‘strcpy’ [-Wimplicit-function-declaration]
   54 |    strcpy(urlbase,  argv[1]);
      |    ^~~~~~
mPresentation.c:17:1: note: include ‘<string.h>’ or provide a declaration of ‘strcpy’
   16 | #include <strings.h>
  +++ |+#include <string.h>
   17 | 
mPresentation.c:54:4: warning: incompatible implicit declaration of built-in function ‘strcpy’ [-Wbuiltin-declaration-mismatch]
   54 |    strcpy(urlbase,  argv[1]);
      |    ^~~~~~
mPresentation.c:54:4: note: include ‘<string.h>’ or provide a declaration of ‘strcpy’
make[2]: *** [Makefile:23: mPresentation.o] Fehler 1

Closes: #79