af-binder: Upgrade

Improvements:
 - addition of supervisor (in devel mode)
 - handling of mimetype
 - integration of systemd watchdog
 - refactor of code handling sessions
 - hooking of sessions
 - started: isolation of systemd event loop
 - started: test of the code

Fixes:
 - exclude directories starting with dot (.) from search
   to avoid issues with debugging libraries
 - memory leaks
 - session leaks
 - segmentation fault on disconnections
 - robustness against time adjust

Bug-AGL: SPEC-1293
Bug-AGL: SPEC-1296
Bug-AGL: SPEC-1303

Change-Id: Idb7908b8a4148a052c72aa662e1d453356d8e40d
Signed-off-by: José Bollo <jose.bollo@iot.bzh>