Dont fail when building translations if resources/localization does not exist, which happens for people building from a git checkout instead of the source tarball
Delete bookmarks from the database when deleting a book

Not sure how I missed this, but the bookmarks where being left in the
database when the books were deleted. This brings it in line with what
happens when using the device to delete a book.

Fixes #1401502 [Delete bookmarks from the database when deleting a book](https://bugs.launchpad.net/calibre/+bug/1401502)