Support custom app logo

[fushar]

Description

Support custom app logo in both admin and client interfaces.

Admin	Client

(Possible) Implementation Details

• Add optional config logo in JudgelsAppConfiguration.

  public interface JudgelsAppConfiguration {
      String getName();
      Optional<String> getLogo();      <-- new config
  

• Add the logo config to judgels-server.yml.example (commented out by default):

  judgels:
    baseDataDir: var/data
  
    app:
      name: Judgels
      # logo: var/conf/logo.png      <-- new config
  

Specific for admin interface

• Implement a new GET /logo endpoint in Michael's IndexResource.
  • If the above config exists, return the logo as image.
  • Otherwise, return the existing logo.
  • Refer to UserAvatarResource::renderAvatar as an example on how to read from resources, and how to return image response.
• Point the logo image URL in admin interface to the above new endpoint.

Specific for client interface

• Implement a new GET /api/v2/web/logo endpoint in Jophiel. Create a new web.WebResource resource, and implement the endpoint there. Implementation is similar to Michael's endpoint above.
• Point the logo image URL in client interface AND favico to the above new endpoint (apiUrl + /logo)
• Remove all existing images in judgels-client, because now we fetch the image from the server.

For deployment

• Add optional app_logo: config in env-example/vars.yml (commented out by default).

  app_version: xxx
  app_name: xxx
  app_slogan: xxx
  app_title: xxx
  app_description: xxx
  # app_logo: var/conf/logo.png       <-- new config
  

• Modify the ansible playbook so that if the config exists, it:

  • copies the file env/logo.png to var/conf/
  • adds the logo config to judgels-server.yml as explained above.