Theme Search: Make theme search more flexible to provide more results

[rachelmcr]

The theme search is very restrictive, which may cause problems for mobile users. Comment from Adam during beta testing:

Searching for a theme name with a space after it returns no results. Compare a search for:
“wedding ”
… with a search for:
“wedding”

Seems like we should work around this since some mobile keyboards automatically put spaces after words when autocompleted or whatever.

It's also worth noting that a search for "wedding" in Calypso on a desktop returns many other themes (such as wedding-topic themes like Forever) that aren't returned in the app's search results. It would be nice to include those kinds of results as well.

[koke]

This is potentially "Low Hanging Fruit". The API for themes includes a tags array which we can store locally and use for search. I tried doing this a couple weeks ago, but couldn't figure out a Core Data crash when using a predicate to search in the tags (any tags contains[c] %@).

[koke]

I figured out the crash: Theme.tags isn't really an array, since there's no such thing in Core Data. It's a "Transformable" attribute and we can't use that for the search. Some possible solutions:

• Make a ThemeTag entity and use that. That'd allow local search but add some overhead on sync to create all the new entities.
• Forget about local, and make search always hit the API for results.