This is an attempt cleanup code and keep the top level config
functions simpler and easy to understand where as move the
notifier related code and logger setter/getter methods as part
of their own struct.
Locks are now held properly not globally by configMutex, but
instead as private variables.
Final fix for #3700
* The user is required to specify a table name and database connection
information in the configuration file.
* INSERTs and DELETEs are done via prepared statements for speed.
* Assumes a table structure, and requires PostgreSQL 9.5 or above due to
the use of UPSERT.
* Creates the table if it does not exist with the given table name using
a query like:
CREATE TABLE myminio (
key varchar PRIMARY KEY,
value JSONB
);
* Vendors some required libraries.
