Multi user features :

->Use Usr App related fonctions instead of Global App related Functions
->Manage properly icon path for each user

BUG=XWALK-2249

Signed-off-by: Sabera Djelti (sdi2) <sabera.djelti@open.eurogiciel.org>
Signed-off-by: Baptiste DURAND <baptiste.durand@open.eurogiciel.org>
Why not use 'TZ_SYS_RW_PACKAGES' and  'TZ_SYS_RW_ICONS' instead?