Added collections for a range of media ratings

I added more collections for creations that fit within a wider range of media content ratings. I try to give content ratings to everything in these collections so that they are safer and friendlier to explore, and appropriate for whatever audience you want to share them with. Together with rated G, which was in the project before, here are all the media rating collections that are available now:

• Rated G, which is the same rating as Everyone (E). This collection has queer zines, games, and other content that are just as family-friendly as a straight person's story of growing up and getting married. They have no swear words. If you're looking for something to share with relatives or a classroom, search in this collection first. It is suitable for all ages to see queer people simply existing, same as everyone else.
• Rated PG, otherwise known as rated Everyone 10+ (E10+). These would be just as family-friendly, except that there were swear words, mild violence, or something suggestive. Usually just a swear word.
• Rated PG-13, which is the same as rated Teen (T). That's for audiences age 13 and up who have had a basic sex education, so that they are prepared to encounter non-explicit references to sex that might be humorous, educational, or a part of a person's life story.
• Rated R, also called rated Mature 17+ (M). These are for adults only because they contain significant violence or sex scenes that serve a narrative purpose.