Rename ActiveRecordModel to ActiveRecordQueries

`ActiveRecordModel` doesn't really feel like a great name, when it just provides two convenient queries. Including some `ActiveRecordQueries` is much clearer about what it does.

@alan could you review? @hmarr @harrison @jackfranklin @mrappleton any objections for this to go into 1.0.0.beta2?
Ugh, sorry I didn't realise this was the readme!