Toolbar, Fixed progressView's flickering, Protocol implementation.

[ADD] Toolbar. Exposed as a property so that it can be hidden.
[FIX] ProgressView's flickering
[ADD] Protocol, which for now, notifies when the user has moved to a new photo.
[ADD] Method to get the selected index.

Signed-off-by: Nikhil Nigade <nikhil@dezinezync.com>