LessonOverview: better display of vocables without kanji
ReinitDBTask.java: major bug: forgot to call sqldb.setTransactionSuccessful(), thus whole reinit_db transactionw as a No-Op

Besides that,

* support for comment lines in .csv files (starting with "#")
* some more debugging output
* Vocable, LessonVocable and Lesson now have sensible toString() methods usable for debugging