feat(feed): a card's menu filters the feed by its channel, and back

Under "Open the channel" a video card's menu (the right-click on its
channel name included) adds the channel to the feed's channel filter, or,
when it is already in, takes it out. Channels OR together, so it widens a
filter that names others, as "Show in feed" does. Not on a channel page,
whose view is that channel already, nor in a live YouTube search or on Home.

frontend/src/i18n/locales/en/card.json

@@ -24,6 +24,8 @@
     "unmarkWatched": "Mark unwatched",
     "unsave": "Remove from saved",
     "more": "More actions",
-    "openChannel": "Open the channel"
+    "openChannel": "Open the channel",
+    "channelFilterAdd": "Filter by this channel",
+    "channelFilterRemove": "Remove the channel from the filter"
   }
 }

frontend/src/i18n/locales/hu/card.json

@@ -24,6 +24,8 @@
     "unmarkWatched": "Megnézés visszavonása",
     "unsave": "Eltávolítás a mentettek közül",
     "more": "További műveletek",
-    "openChannel": "Csatorna megnyitása"
+    "openChannel": "Csatorna megnyitása",
+    "channelFilterAdd": "Szűrés erre a csatornára",
+    "channelFilterRemove": "A csatorna ki a szűrőből"
   }
 }