Absolute links to webdiplomacy.net (and other references)

[diptobi1]

I just noticed, that there are currently direct links to the main web dip server. Even if you are on a fork like vdip.

Take the following picture of how the registration mail for vdip currently looks:

(Ignore the lower half. There is apparently still an issue with the last code merge.)

The link to the rules and the password finder are hard coded (though the latter was already changed in the past). As a suggestion it would be much better to make it dynamic as it is already the case for the validation address (e.g. with $_SERVER['SERVER_NAME']).
The link to the webdip discord server is hard-coded, too. That could be put to the configs, perhaps?

Additionally, what would be a very neat feature for the future, though certainly not that urgent, would be a configurable website name set in the configs. Then all appearances of "webDiplomacy" could be replaced by the config variable. That would make customizing webdip much easier for forks.
After the last code merges on vdip the references to vDiplomacy and webDiplomacy are quite a mess.