Put skeleton and solution branches in side-by-side directories

* The original skeleton 'lib' directory had all of the files nested under an extra 'active_record_lite' folder, so I moved them out and altered line 4 in 'db_connection.rb' accordingly.
* Rearranged the instance methods in '01_sql_object.rb' to line up better with the instructions
* Added missing params argument in #initialize in '01_sql_object.rb'
* Changed phase numbers to line up with instructions