Add chain-able `where()` conditions.

E.g. .where( "status = 'active'" ).where( "tag_uid = 'A342'" )

This mimics ActiveRecord:

Client.where("id = 5").where("id > 2").to_sql
=> "SELECT `clients`.* FROM `clients`  WHERE (id = 5) AND (id > 2)"
Merge branch 'master' of github.com:joshuapinter/ActiveAndroid
Merge pull request #190 from joshuapinter/master

Fixes Issue #165 by Allowing Chain-able `where()` Conditions.