advanced reboot: add soft reboot option

Adds a "Soft reboot" option which restarts zygote, as requested in JIRA
CYAN-3998

Change-Id: Ia6e5ed9b053e1c5ebd1fc55e5692858b97f7e0fc
Signed-off-by: Roman Birg <roman@cyngn.com>

Conflicts:
	core/res/res/values/cm_arrays.xml
	core/res/res/values/cm_strings.xml
ShutdownThread: set soft reboot trigger accordingly

Change-Id: I72bd52aa1492d356e368e8c60897002c1f110172