Move configuration methods to class methods

[eduardoj]

We don't need to retrieve the values stored in the singleton record of the table configurations in the database for none of the ldap_enabled?, proxy_auth_mode_enabled? and amqp_namespace methods.

Moving each method to the class methods section prevents from performing unneeded database queries.

For reviewers

Before

Taking the home:Admin project page as an example, browsing http://localhost:3000/project/show/home:Admin and taking a look at the frontend log resulted in:

• 3 direct SQL queries to the database:

  Configuration Load (0.5ms)  SELECT `configurations`.* FROM `configurations` ORDER BY `configurations`.`id` ASC LIMIT 1
  

• 10 cache hits:

  CACHE Configuration Load (0.1ms)  SELECT `configurations`.* FROM `configurations` ORDER BY `configurations`.`id` ASC LIMIT 1
  

After

Browsing http://localhost:3000/project/show/home:Admin resulted in:

• 3 direct SQL queries to the database:

  Configuration Load (0.5ms)  SELECT `configurations`.* FROM `configurations` ORDER BY `configurations`.`id` ASC LIMIT 1
  

• 7 cache hits (3 less than before):

  CACHE Configuration Load (0.1ms)  SELECT `configurations`.* FROM `configurations` ORDER BY `configurations`.`id` ASC LIMIT 1
  

[obs-bot]

Review app will appear here: http://obs-reviewlab.opensuse.org/eduardoj-refactoringconfiguration_class_methods

[eduardoj]

@hennevogel, I modified the code. Please tak a look again.