load user config file

- load user config in application.rb
- basic authentication password is loaded from the included configuration
add sample of user_config.yml
ignore user_config.yml

- because user_config.yml is specific for each environment, it should
  not be included in the repository
implement read_only mode
update doc about READ_ONLY mode
updated doc about config
rename the key of config file
Merge pull request #288 from crest-cassia/user_config_file

User config file