[#161] Add report issue and clone link in the configuration

Add two new optional configurations:
 - blue.client.issues-url: the link to the issue manager
 - blue.client.clone-url: the link to the source code of the project.

These two new configurations are also integrated in the client. If these configurations are not set, the links are removed from the UI. 

The configuration manager has been improved to facilitate the access to configurations while supporting a larger number of configurations.