ifmap: added IFMapConfigListener template

Functionality similar to one provided by BgpConfigListener is needed in
other parts of the project. By abstracting it I hope to avoid
copy-paste.

Change-Id: I49e3b1c2a1ba35b6458780301219516d21d6d7a0
Signed-off-by: Mateusz Zalega <mateusz.zalega@codilime.com>
Merge "ifmap: added IFMapConfigListener template"