Changes targetUrl config options and gets app config file via a service

The app config file will now be served by the backend. It will instead
be a java properties file where target url config options will now be
as follows:

targetUrl.pattern // Pattern to look for in the target url
targetUrl.replace // String that will be used to replace the target
                  // url value

For example:
targetUrl.pattern:(.*?)(.com)
targetUrl.replace:$1.net