fb: add accessibility events to lockscreen slider and shortcuts (1/2)

beside that it is nicer for ppl using talkback eg and get clear
instructions this solves as well a fc in settings lockscreen targets
when using accessibility services

Change-Id: I03014892d30491b1d126e61a6891393416e4b1be

Conflicts:
	core/res/res/values/slim_symbols.xml
	packages/Keyguard/src/com/android/keyguard/KeyguardSelectorView.java
	packages/Keyguard/src/com/android/keyguard/KeyguardShortcuts.java