URL handling in bukuserver

[LeXofLeviafan]

As of now, bukuserver creates hyperlinks to "invalid" URLs (those without a netloc) – this should be amended.

In addition, URL input validation in the UI form differs from buku: buku only rejects empty values, while bukuserver rejects any blank URLs (i.e. whitespace-only).

[LeXofLeviafan]

…Note: I've changed blank check in the code, but whitespace-only URLs are still rejected by the "required" validator in the form itself.

Nevermind, there's an alternative InputRequired validator (which is actually preferred according to the docs) that allows whitespace-only inputs.