Add support for Pride campaigns

[misaochan]

@Ladsgroup suggested to me that he would be interested in working on a "Pride" version of the app for events like pride parades - when they upload the pictures, it would add some categories related to that campaign.

I reckon that this could eventually even be generalized to all campaigns. For instance, if Wiki Loves Pride is on, we will already be displaying it as "News" on our main screen (see https://github.com/commons-app/campaigns ). So instead of just bringing the user to the campaign's site when they tap on the news banner, we could bring them to a section in Settings where they can opt in to the campaign perhaps?

All thoughts welcome. :)

[Ladsgroup]

Given that almost all pride parades have been cancelled this year. I think it's lower priority now :(

I will try to tackle it when I have a little less in my plate.