Get as much information from siteinfo as possible

Properly fixes #74.

Algorithm:
1. Try all siteinfo props. If this gives an error, continue. Otherwise, stop.
2. Try MediaWiki 1.11-1.12 siteinfo props. If this gives an error, continue. Otherwise, stop.
3. Try minimal siteinfo props. Stop.
Not using sishowalldb=1 to avoid possible error (by default), since this data is of little use anyway.