[Feature] Improved server-endpoint form for Mobile

The feature Currently, when the app is open for the first time, the user is asked to fill in the endpoint for the server. It must always start with http:// or https:// and end with /api, and currently, there is no "self-correction" for this. 1. When http:// or https:// are not at the beginning of the input string, the App should automatically try to add https:// in front, if https:// has no response (so, this doesn't apply if a certificate is invalid), the app will try with http:// 2. If there is a trailing slash on the URL, it should be automatically stripped before trying to contact the API, or, to have better compatibility with some reverse proxies, an info-message should be shown reporting that. Eventually, we could apply the same principle as before and test both ways, so that "what ever works is good". 3. If the input string doesn't end with /api, it should be automatically added or reported with an info-message. Again, the first behaviour…