Show contact add requests in chat

[mwild1]

Describe your feature proposal Currently when a contact adds you to their contact list, a temporary notification is shown, but there is no other UI in the app. We will replace this notification with a widget in the chat view to approve/decline the contact subscription request.

Requirements

• When a subscription request is received, do not show a notification
• When a subscription request is received, add a new empty chat to the chats list for that JID (if such a chat does not already exist)
• When the user opens a chat that has a pending subscription request, display a bar in the chat view (see mockup)
• If the user taps "Approve": launch the "Add contact" dialog, pre-filled with the account and contact JID.
• If the user taps "Ignore": reject the subscription by sending an 'unsubscribed' presence
• Either action should dismiss and hide the bar from the chat view
• The user should still be able to send/receive messages while the bar is visible
• The bar should adapt to light/dark appearance as necessary

Mockup