Implement k_gen_storage:read operation to return entries in [{Key, Value}] format
Implement k_mongodb_storage:read to return all entries
Make k_mongo_db to the default storage engine
Implement get all api calls

Implement:
1. k_aaa_api:get_customers().
2. k_config_api:get_networks().
3. k_config_api:get_networks().
4. k_config_api:get_providers().
Merge branch 'feature/dk_gen_storage_read_all_17486' into develop
fix rebar dependencies
add select all gtw handler
add return all networks method
Add return all providers method
Add return all customers method
Add msisdn field to http get customers method
Merge branch 'feature/as_return_all_method_for_http_17319' into develop
Fix xml customer return format
Implement read all
Merge branch 'develop' of github.com:PowerMeMobile/kelly into develop
Add name & state fields for customer
Merge branch 'feature/as_add_customers_fields_17523' into develop
Merge branch 'develop' of github.com:PowerMeMobile/kelly into develop
Enable sync
Merge branch 'develop' of github.com:PowerMeMobile/kelly into develop