Mime handling for zstd

EasyOS has the zstd utility, however lacks proper mime handling. Like, assigning a mime-type, handling when click on a .zst or .zstd file, support in Xarchive.

I have run out of steam to explain all the changes, just take it as done.

Zstd mime type:

https://www.iana.org/assignments/media-types/application/zstd

Thanks to peebee for zstd support in Xarchive:

http://www.murga-linux.com/puppy/viewtopic.php?p=1048178#1048178

...I only used the Xarchive wrapper, usr/lib/x86_64-linux-gnu/xarchive/wrappers/tar-wrap.sh, from peebee's tarball. All of the mime-handling I implemented independently.

Note, /usr/local/bin/pkghandler.sh has been expanded to handle all tarball types, that is, .tar.gz, .tgz, .tar.xz, .txz, .tar.bz2, .tbz2, .tar.zstd, .tar.zst. A left mouse click on any of these file types will run 'pkghandler', which tests whether the tarball is a binary package (is not a source package) and if so, asks if want to install it or open it in Xarchive. If not a binary package, immediately opens in Xarchive.   

Tags: easy