Do not capitalize page titles when importing dump

Capitalization of titles led to duplicates in SQL key for
namespace and title if a corresponding upper-case title was
already contained in the dump.

WikiTitle now has a new method parseCleanTitle which can be applied to
clean titles like those contained in Wikipedia dumps. Capitilization can
now also be disabled in the constructor of WikiTitle.
Update parameter names in documentation of WikiTitle
Clarify check for explicitly given namespace
Merge pull request #232 from dfleischhacker/preventduplicates

Do not capitalize page titles when importing dump