Add UI tests to TimelineTableView

[pixlwave]

We should be able to run UI tests to detect whether any expected behaviours of TimelineTableView have been broken. The following tests are proposed:

• A room with just 2 messages - these should be aligned to the bottom.
• Above with a small back pagination and an incoming message - the messages should remain bottom aligned.
• Back paginating when the timeline isn't right at the top - no visible change should be seen.
• Back paginating when the timeline is at the top - a small change might be visible to the top item.
• A new message is received whilst at the bottom - the timeline should be scrolled to reveal the message.
• A new message is received whilst scrolled up - no visible change should be seen.
• Showing the keyboard whilst at the bottom - The last message should be shown above the keyboard.
• The same as above with a timeline that contains lots of images.
• Showing the keyboard whilst scrolled up - The last message should be hidden behind the keyboard.
• Receiving a pagination response that succeeds but without any items - the Syncing indicator should be hidden. (syncing indicator removed)

[pixlwave]

Closed by #380.