Post swiper, full screen activity component, pagination in discovery v2, general fixes

• Clean up current components
• Fix composer icon shadows
• Add support for pagination into discovery v2
• Create a full-screen component view for activities with support for editing and actions
• Create a bottom popup for the comments
• Create a performant swiper that receives a FeedStore to show posts and loadMore support
• Clean up code and test.
• Fix scroll and touchable into comments popup (Android)
• Fix keyboard issues in comments popup (iOS)
• Change styles for comments to be closer to new designs
• Remind open stacked composer if the post is inside a stacked screen
• Channels and groups rendering into discovery v2
• Tapping a hashtag should open discovery v2 search

closes #2215 (closed) #2253 (closed) #2249 (closed) #2168 (closed) #2244 (closed) #2257 (closed) #2256 (closed) #2246 (closed)