1- Removed the additional verification we placed last semester to block audio and video testing
2- Made sure that we can pin and unpin videos and audios in both 1-1 conversation and groupchat

1- Added Audio stub object to pinned messages
2- Added pinned audio xml views
3- Introduced isAudio and isVideo to pinnedMessagesAdapter
4- Refactored the way pinned images and videos are being verified in pinned Messages adapter

1- Added Document stub object to pinned messages
2- Added pinned Document xml views
3- Introduced isDocument() to PinnedMessagesAdapter
4- added some code cleanup in PinnedMessagesAdapter class