[lmi] PATCH: use compressed .mst files

[Vadim Zeitlin]

 Hello,

 Sorry for the time it took to create it, especially considering how
trivial the changes are, finally, but here is the long-promised PR
implementing support for compressed template files:

        https://github.com/vadz/lmi/pull/100

 The code changes are really simple and the only potentially questionable
thing is the use of access() to test for the file existence, but this is
how lmi seems to do it elsewhere, so I did it here too, even though this
code could use wxFileName::Exists() instead or even just try to open the
file input stream and rely on the error generated by it -- except that this
would have required dealing with wxLog and lmi code does not do this
anywhere else, so I didn't do it here neither.

 I spent more time on makefile changes than on the code because I couldn't
figure out what would be the best or, maybe, least objectionable way of
dealing with installing the template files. Initially I really wanted to
rely on make for updating them, i.e. have a "%.zst: %.mst" rule, but this
required many changes to the "install" target and, after looking at them, I
wasn't sure if you'd like it, so I've finally implemented the current
version which uses this "-e -o -nt" construct explicitly instead of relying
on make. This is a bit silly but OTOH it's not that bad and like this my
changes could be limited to pure additions, which will hopefully make them
easier to review and integrate.

 But please let me know if you'd prefer the other version or if you have
any other comments or questions, of course.

 Thanks in advance,
VZ