SJOSearchableFetchedResultsController additions

[lukestringer90]

I was using SJOSearchableFetchedResultsController in a scenario where I wanted to display a section index for a table view. So I made some changes to facilitate this. Mainly the ability to override a method in your subclass to specify the sectionKeyPath that should be used when constructed new NSFetchedResultsControllers.

This worked fine but then I released that the table view section index should not be displayed when the user is searching. So the newFetchedResultsControllerWithSearch: method takes this into account by ignoring any specified sectionKeyPath if the user is searching. This necessitated the searchIsActive property, which is set to YES when searching begins, and NO when searching is cancelled.

I also added the ability to construct a SJOSearchableFetchedResultsController with a managed object context if you want to use SJOSearchableFetchedResultsController without being depending on an SJOStore instance.

So to use a section index in a SJOSearchableFetchedResultsController subclass:

- (NSString *)sectionKeyPathForSearchableFetchedResultsController:(SJOSearchableFetchedResultsController *)controller {
    return @"uppercaseFirstLetterTitle"; // the sectionKeyPath
}

- (NSArray *)sectionIndexTitlesForTableView:(UITableView *)tableView {
    // No section indexes if searching
    if (self.searchIsActive) {
        return nil;
    }
    return self.sectionIndexes;
}

 (NSString *)tableView:(UITableView *)tableView
titleForHeaderInSection:(NSInteger)section
{
    return [[[UILocalizedIndexedCollation currentCollation] sectionTitles] objectAtIndex:section];
}

- (NSArray *)sectionIndexTitlesForTableView:(UITableView *)tableView {
    return [[UILocalizedIndexedCollation currentCollation] sectionIndexTitles];
}

- (NSInteger)tableView:(UITableView *)tableView
sectionForSectionIndexTitle:(NSString *)title
               atIndex:(NSInteger)index
{
    return [[UILocalizedIndexedCollation currentCollation] sectionForSectionIndexTitleAtIndex:index];
}

[blork]

Great stuff. Might as well remove the Store initialiser and property, since all it needs is the context.
If we're gonna release SQK, maybe we should add this to it and I'll just deprecate SJO?