don’t copy untranslated source files

Signed-off-by: Chris Warrick <kwpolska@gmail.com>
use new-style metadata in importers

Signed-off-by: Chris Warrick <kwpolska@gmail.com>
add post.newstylemeta attribute

Signed-off-by: Chris Warrick <kwpolska@gmail.com>
fix tests for get_meta

Signed-off-by: Chris Warrick <kwpolska@gmail.com>
join tags

Signed-off-by: Chris Warrick <kwpolska@gmail.com>
Added support for GALLERY_FOLDERS (replacing GALLERY_PATH in a similar manner as LISTINGS_FOLDERS).
Fixed flake8 warnings (forgot to import sys, and forgot to remove left-over stuff after refactoring).