add migration creating func_key_destination_extension
migrate existing voicemail function keys
pregenerate entries related to voicemail in fk and fk_dest_extension
add default data in func_key_dest_extension
fix branch conflict
sed 's/extension/service/' (except for extensions table)
move voicemail types into constants
fix branch conflict in alembic migration script
fix branch conflict
use standrd sqlalchemy construct
merge revision branches
add the version to the migration scripts