More explicit filter cue for drop downs in article section

Since default of article filters are for all types, might be better
to label what the current state of drop down filter is instead of
a "Please select".

This matches up with the "All articles" filter.
Add translations for new article filter defaults

Guessed from parsing through Google Translate.

Have left those with no confidence in getting
a close to correct translation as blanks.

Hopefully that means the rest are valid.

- Danish               - French
- German               - Italian
- Lithuanian           - Norwegian
- Polish               - Romanian
- Simple Chinese       - Spanish (Mexican)
Merge pull request #111 from randomecho/admin-article-filters

More explicit filter cue for drop downs in article section