[O] ditaa and plantuml in PATH

[Alexey Shmalko]

Hi!

I use NixOS and ditaa is globally installed. That means I have ditaa
executable in PATH but no easy way to find a ditaa.jar file. There is
no way to instruct org-ditaa to use the specified executable (it
requires java and path to the ditaa jar file). Note also that I don't
have java in PATH.

I would like org-ditaa to use ditaa executable from the PATH. Same
goes for org-plantuml.

Regards,
Alexey Shmalko