systemui: open add tile dialog

Shows the "add tile" dialog QuickSettingsTiles activity when the user press
the add tile button in the system bar

Change-Id: I974f50806c724a400485de54589accbdde4bf70d
Signed-off-by: Jorge Ruesga <jorge@ruesga.com>
Revert "systemui: open add tile dialog"

This reverts commit f9951ad9276852b5e6154a54349996a8ddbf1812.

Change-Id: If3211aceab3c92028ab07508c40bfff0813cdf34