contactrequest: add ui for managing pending CR

Those modifications are only a part of the contact request
system. In details :
 * A panel on the left displays the incoming CRs for the
   selected account.
 * A tab system makes it possible to switch between the
   smartlist and the pending CR list.
 * When a CR is selected, a view of it is shown on the right
   with 2 buttons. One for accepting it, the other for
   discarding it.
 * The stylesheet is updated to adapt the new widgets
   with the design of the client.
 * When selected account is changed, we get back to the
   welcome page

Change-Id: I86dc7f32105c0454b0e4d002b6a78fde2c581a44
Reviewed-by: Olivier Soldano <olivier.soldano@savoirfairelinux.com>