Set panel launch mode to singleInstance and fix animation

Set panel launch mode to singleInstance to avoid panel can show up
infinite time when user keep launching panels (Easy repro by
pressing volume hard key > settings again and again).

After changing launch mode to singleInstance, we will need to do
some refactors, to avoid weirdness when adding/changing/closing
panels:
1. Move and refactor logic in SettingsPanelActivity#onCreate.
   We will need onNewIntent here to handle Panel launching, since
   we only have one instance of SettingsPanelActivity now.

   Also do refactor here to reuse the PanelFragment instead of
   creating one every single time, to better handle the exit
   animation, avoid janky exit behavior from the old PanelFragment

2. Move logic from PanelFragment#onCreateView, to reuse it when
   updating panel content.

   Also add exiting animation when we are transitioning the panel
   from one to another.  Also add alpha animation to make it move
   more smoothly.

3. Adding flags to launch see more intent in settings.

Fixes: 131225920
Fixes: 131254399
Test: manual
Change-Id: I93d3708bd02a2d736e38685475f2d9988ef62d31