Mesh: Apply stabilization fixes in CAPI

Mesh: Apply stabilization fixes in CAPI

Some of the notable changes are following-

1. Add 'Model Configure AppKey event handling'
2. Fix bug in fetching model from element
   [Fixed wrong handling og GSLists]
3. Apply exception handling in deleting NetKey from a node
   [Application crash in case of invalid NetKey handle]
4. Fix bug in handling appkeys bound to a NetKey of a node
   [Return AppKey(s) bound to NetKey, instead of reurning ALL AppKeys]
5. Fix application crash due to double free
   [Double Free of Model AppKey List items]

Change-Id: Icea2e305d5cd2059b2db35d80aa269b9d547b176
Signed-off-by: Anupam Roy <anupam.r@samsung.com>