Added imgur.com support, works also on albums.

Even though on albums only the last downloaded picture will be shown in queue. If I get to know how I can add multiple files to a package from withtin a plugin I'll fix this.
Try to replace lines 17-20 with this:
```python
f = lambda url: "http://"+ re.sub(r'(\w{7})s\.', r'\1.', url)
urls = map(f, re.findall(self.LINK_PATTERN, self.html))
```