better POSTS/PAGES in import_wordpress

Signed-off-by: Chris Warrick <kwpolska@gmail.com>
Can import a exists ipynb file
fix #1385 -- add -i, --import option to new_post

Signed-off-by: Chris Warrick <kwpolska@gmail.com>
Added option to make indexes paths more pretty when both PRETTY_URLS and INDEXES_PRETTY_PAGE_URL are set to true.
Made prettified index page URL configurable.
Made pretty index page URLs better configurable and translatable.
Moved create_redirect from plugin into utils.
Adding redirect in case INDEXES_PAGES_MAIN == True and INDEXES_PRETTY_PAGE_URL is set.
Fixed argument to utils.config_changed.