Ignore first crash dialog.

By default, no longer show the crash dialog the first time an app
crashes. Instead, only multiple crashes will show by default.

Add Settings.Global and Settings.Secure flags to toggle this behavior.
Settings.Secure value is controlled via a setting in developer options.

Ensure Settings.Secure is backed up but Global value is not.

Bug: 63703353, 70640329
Test: SettingsBackupTest, manual crashing with a test app

Change-Id: Ib0a66cabdf60aad5e60eded9bfb96e3126bf032f