Sotw entry validations

[Robin-M]

• [x] The following entry (equal to the template) is accepted:

artist: title: anime: url:

I think the field values (after the colon) should match 0 or more spaces followed by at least 1 non-space character. So if someone forgets to fill in one field the entry is rejected.

• [x] Illegal streaming sites are accepted. Only youtube.com and youtu.be should be allowed.

• [x] Nice to have: search the artist and title in the list of winners. If a full match is found, reject the entry. Of course this will not prevent all duplicates because of spelling or name order, but most of us probably just copy the values from MAL anyway.

[ihulsbus]

Additionally we need to make sure the SOTW code also forces the rules of the STOW. I'll create an new issue for this