Shuffle cachemgr.cgi.8 into tools/ with cachemgr.cgi code

Shuffle cachemgr.cgi.8 into tools/ with cachemgr.cgi code

To perform this shuffle the SUBSTITUTE make code pushed into a sub-include
at doc/manuals/Substitute.am for shared use.

Also clean up the manual titles to reflect the binary they apply to
rather than the generic Squid project release name.

The use of generic @SYSCONFDIR@ and specific filenames allows the
translation strings to be more specific, readable for translators and
reduces Makefile complexity at once. squid.conf etc are widely mentioned
and used enough that allowing for alternative names at this point seems
meaningless.