Announce maintenance time in the API

[Akron]

Following the suggestion by @kupietz , maintenance time should be announced in the Welcome-Message of the API (/api/v1.0/), which is always shown at startup by the major clients. To make this possible, maintenance announcements should be read from a file separate from the news and returned in reasonable formats both on the front page as well as integrated in the welcome message. The welcome message therefore - usually only transferred by the proxy - needs to be rewritten for this purpose.