Socket.io logic for real-time file sharing

[sojharo]

part of https://github.com/Cloudkibo/Android/issues/162

This is parallel with #460

1. When sender has sent the file to server, server should use socket.io to inform the recipient to download the file.
2. When recipient has finished downloading the file and calls confirmation endpoint of server (in #461 ) then server should use the socket.io to send the status to sender that file has been downloaded.
3. If sender is offline and didn't receive the status, then status should be updated using http endpoints during sync. We should leverage the https endpoint which gives out the chat messages. The file entry in chat table would have its unique id and status which would be updated.

Note: The database table discussed in #460 will only store temporary entries (meta data of file and address on server) and remove them when download is done. But persistent entry of file sharing would be part of chat table as file would be shared as one of chat message type on chat window.

[sojharo]

I have added the socket.io code for server side. Now, file sharing will be known in real time as well.

[jekram]

Thanks

[jekram]

https://github.com/Cloudkibo/Android/issues/169