Added "checkpoint" articles

[mbjackson7]

This PR makes it so that there can be checkpoint articles, which are articles that must be visited in order before reaching the ending article.

The startingArticle and endingArticle have been replaced with the articles array and targetArticle, which specifies the index of the article the user is currently looking for. The current target article will appear in yellow text on the wiki page to be easily identifiable.

Users can add and remove articles directly from the settings pages.

Translations have been provided for the new required controls.

[B0und]

Hey! Thank you for your contribution! I really appreciate it.
I haven't looked into the PR that much, but there seem to be a couple of issues:

1. There is an error in the console when I start the dev server
2. If you select some starting and ending article -> press add new article -> delete the second one. You can now start the game, but there is no win condition.
   Also i havent been able to reproduce this yet, but some combination of deleting and adding articles resulted in an error (I think it was something about too many calls to history API).

I`ll try to take a more thorough look at it on the weekend.

[mbjackson7]

I'll take a look and see if I can figure those out when I have time as well.