Support hosted PlantUML server

[codeprefect]

Nice work on the plantuml rendering, but I think it will be great to also allow users to use their own PlantUML servers.

This approach is common with most PlantUML viewers out there because some users definitely have concerns about pushing their private data to a server out there.

See here for inspiration.

[colladovictor]

The link doesn't seem to be accessible. I get returned the following message within a html page:

This site can’t be reachedCheck if there is a typo in qjebbs. DNS_PROBE_FINISHED_NXDOMAIN .

Please verify &/or update the link.

[codeprefect]

Hi @colladovictor , I have updated the link