Adding .htaccess files to prohibit access to critical directories, e.g., db/

This commit would fix a critical security hole that allows anyone to access the sqlite database file by simply pointing their browser to: https://DOMAINNAME/wallabag/db/wallabag.sqlite (previously https://DOMAINNAME/poche/db/poche.sqlite).
See: http://invisibletower.de/2014/wallabag-auf-dem-uberspace/ and http://classmplanet.de/poche-on-uberspace/