add delegate for pending contact requests

This change adds an item delegate used to display every
elements in the pending contact requests list.

The displayed view is consistent with the existing smart
list view. It shows the RingID of the sender and its picture.
This last one is currently the default picture but is expected
to become the one embedded in the payload if any.

Change-Id: Idc7afb5c6bfcda7bce67dfd042a28f9789506815
Reviewed-by: Olivier Soldano <olivier.soldano@savoirfairelinux.com>