This allows the user to run a keyword search and then change the sort
order. `Default` is interpreted as `Relevance` if a query is present,
`Newest` if not.
Here's what's in `IndexableText` right now:
1. Title
2. Collections
3. Authors
4. Tags
5. LocSubjects
6. TocEntries
Here is the proposed new ranking:
```
10 * Title +
8 * Authors +
3 * Collections +
IndexableText
```
New indices for existing DBs:
```
ALTER TABLE `Ebooks` ADD COLUMN `IndexableAuthors` text NOT NULL;
ALTER TABLE `Ebooks` ADD COLUMN `IndexableCollections` text NULL;
ALTER TABLE `Ebooks` ADD FULLTEXT `indexSearchTitle` (`Title`);
ALTER TABLE `Ebooks` ADD FULLTEXT `idxSearchAuthors` (`IndexableAuthors`);
ALTER TABLE `Ebooks` ADD FULLTEXT `idxSearchCollections` (`IndexableCollections`);
```
For different reasons, setting multiple="multiple" on <select> tags
doesn't work on Kobo and Kindle browsers.
On Kobo:
* the <option> tags don't appear
* the <option> tags in other <select> tags also don't appear
* the labels on the other form elements get offset
On Kindle:
* the full set of <option> tags don't appear, and the <select>
won't scroll to show them
