- cleaned up const qualifiers in interfaces

- cleaned up const qualifiers in interfaces
- added Ctrl-L screen refresh
- fixed segfault in test.c when listbox items are selected
- accessibility: made newt useable with monochrome terms (#60931)
- leave the symbols in the libs (#60400)
- fixed grammar in tutorial (#63496)
- removed obsolete URL reference in tutorial.sgml
- error checking (curcomp exists) for formEvent, newtFormGetCurrent,
  removed fifty button limit (#59027)
- allowed the test progs showchars and showkey to be build via the makefile