gatt_client: drop subclient struct and id. pass in callback for requests. new gatt_client_listen_for_characteristic_value_updates for notifications and indications with client provided storage

rename sdp -> sdp_server

split remote_device_db into btstack_link_key_db and btstack_device_name_db

btstack-config.h -> btstack_config.h

structure btstack-config.h

prefix memory_pool functions/types with btstack_

prefix memory_pool files with btstack_

create service_record_item memory pool

fix paths after source reorg

use singular for root level folders