Take out hardcoded loklak.org and api.loklak.org URLs and add them in config file

[Mario Behling]

The search on https://github.com/fossasia/loklak_search/search?q=api.loklak.org&unscoped_q=api.loklak.org shows a number of hardcoded URLs.

If we want to test this frontend with another server it is not easily possible because of hardcoded URLs. Please change this in a way that the server URL is stored in a config file instead.

Ensure the following can be changed easily through changing a config file:

• The URL of the API server
• The URL of the loklak.org service itself
• The logo image on all pages (If the image is changed in the config, it should change everywhere)