Fix bug on last remaining card introduced in 0.9.5.6.

* Two more 'earliest card due in future' fixes
* Use temporary working directory when generating latex (fix OSX problems)
* Fix cards being marked as mature too early
* Mature cards are now defined as cards with an interval over 21 days, instead of cards with a previous interval of over 9 days
* Japanese translation updates from IanL and wrightak