Add support for user specific database configuration

Author: rastating

db/env.rb

@@ -2,7 +2,10 @@
 
 ENV['WPXF_ENV'] = 'development' unless ENV['WPXF_ENV']
 
-db_config_path = File.join(__dir__, 'config.yml')
+# Use the configuration file found in ~/.wpxf/db/config.yml primarily
+# and fall back onto the packaged configuration in db/config.yml.
+db_config_path = File.join(Wpxf.home_directory, 'db', 'config.yml')
+db_config_path = File.join(__dir__, 'config.yml') unless File.exist?(db_config_path)
 db_config = YAML.load_file(db_config_path)[ENV['WPXF_ENV']]
 
 if db_config['database'].nil?