allow entering of MUD-URL rather than uploading directly the mudfile

[elear]

requested by @mcr

[Vafa-Andalibi]

This can be further improved by adding the possibility of bookmarking the result, so the resulting URL might look something like:

https://w2.mudmaker.org/vmud?mudfile=https://iotanalytics.unsw.edu.au/mudprofiles/NetatmoCameraMud.json