Migrate UsageStats to Spa

The UsageStats page is for testing only, cannot entry through Settings
Home, but is accessible by enter *#*#4636#*#* in dialer.

Migrate UsageStats to Spa for both improving the UI & performance.

Fix: 244675756
Bug: 235727273
Test: Manual with Settings App
Change-Id: I6ec6e233075a3f79ac1231aecafabf2a71dac716