Allow use of non-random pad names

[digital-codes]

We would like to use pads with specific names, like codeforka-2020-03-29
For the moment I accomplish this by overweriting the random token with the name of the pad in lib/OwnpadService.php like so:
$padID = explode(".pad",$padname)[0];

It would be nice to have this as a configurable option from the ownpad server settings. This also relates to issues #78 (configuablesuffix) and #7 (existing pads). I tried this for opening existing pads and it works OK. I would be willing to help on the settings GUI once I know where to look for the files.

[fwolfst]

Small correction: its apps/ownpad/lib/Service/OwnpadService.php (line 43).