Allow items to be both watched and in the watchlist

[etoome]

• Movie: Show the button to add an item already watched in the watchlist
• Show: Show an option to add an item already watched in the watchlist
• Movies & Show: In the watchlist, list all items even those already watched

[michaldrabik]

Probably won't happen as the base of everything in Showly is that items can only be in either watched/watchlist/hidden at one time.