Rearrange a few settings into System category page.

- Use activity-alias to define which activity shows up in what category.
  We choose activity-alias because it creates a reference to UI we need
  without having to define a new set of intent-filter and/or category
  keys. This reduces maintainence in the long run. We should merge
  metadata from activity-alias into targetActivity when cleaning up.

- Created new System dashboard activity that hosts all system category
  tiles dynamically, and a static tile for checking system update.

Bug: 31781480
Test: manual
Test: make RunSettingsRoboTests -j40
Change-Id: Ia2d762e3e1aebd17423a395c5e6c286dc3326492