Query "contains" for database properties

[reedspool]

When searching certain text based properties, it would be quite useful to query for text containing the search term. As it stands, only queries for text properties which exactly equal the search term can be queried. Examples of properties are the following: Tags, 'game' in 'games'; Author, 'Last' in 'FirstLast'; Description, 'fun' in 'This app is totally fun!'

[derrell]

Assigning this to Reed. This will allow Reed to learn about the differences in the implementations of the (currently) two backends (simulated and App Engine).

Before beginning this, we should better document what the criteria map looks like. Reed, let's discuss.