* Normalize spaces to underscores when saving other names. Preserve case
since case can be significant.
* Fix WikiPage#other_names_include to search case-insensitively (note:
this prevents using the index).
* Fix sources to return the raw tags in `#tags` and the normalized tags
in `#normalized_tags`. The normalized tags are the tags that will be
matched against other names.
If the yande.re or konachan.com post has a source from a supported site,
for example Pixiv or Twitter, then delegate the artist and commentary
lookup to that substrategy.
Only do this for sources from recognized sites, not the null strategy.
