Copy swt.jar to a directory in ${work} rather than ${mac.dir} as there's
no need for droppings all over the build tree. Also cleaned up building
${maczip} a bit to avoid extra file copying, to put the uncompressed
.app in ${dist}, etc. Removed some cruft from .gitignore while I was at
it.
The conditional nature of building macBundle kind of bothers me a little
since if you have the correct swt.jar (which we could provide and have
in some versions of the build system), you could build self-contained
packages for macOS and for Windows. A self-contained package for Linux
is also possible, but doesn't make much sense as Linux software
installation routinely involves installing dependencies, either manually
or automatically.
