Fix some missing header includes to make headers stand-alone
presolve: Add missing function declarations in header file

A handful of non-static functions in presolve.c are missing from the
header file.
qsopt: Make TYPE_grab_cache() public since it is used in exact.c

Changes TYPE_grab_cache() to TYPE_QSgrab_cache() and adds the
function to qsopt.h.
exact: Include header files instead of repeated declarations
Makefile.am: Only generate template symbols from header files

Since all global symbols should now be defined in header files it is
sufficient to generate the list of template symbols from these files.