404 status page for unmatched URLs, 410 status page for deleted blogposts

[fumiX-RMI]

If blog entries are linked or bookmarked from outside the system they may get deleted and still be referenced. At the moment there will be just a blank screen.

• [x] show 404 Not Found error page for unmatched URL
• [x] show 410 Gone error page for deleted blogposts

[floscher]

There should be a general 404 page, any unmatched URL at the moment leads to a blank page (also currently returns a 200 status code).

I'm not sure, if we should make a special case for deleted blogposts. What would that page display, apart from "Once upon a time there was a blogpost here"?

[floscher]

On #52 there is a basic 404 page now

[thooyork]

improved / cleanup general 404 page respond 410 on ids that doesn't exist (anymore)