Added NSPredicate query to searchFiles() method

searchFiles() method now moved to FileProviderBasic, where it belonged. Now there is two version for searchFiles(), one of them gets String for query to search within files name, also you can set a NSPredicate object to query to filter files based on properties like size and modification date, please read inline help for sample predicates.

Also:

• all methods are now open to become overridable
• Fixed Documentation errors about urlCache