Support static in addition to dynamic shadows.

ShadowOverlayContainer may be configured to use static or dynamic shadows.
Adds new Settings with key PREFER_STATIC_SHADOWS.
Settings are maintained staticly so they only need to be generated
when a new app process is created.
Some settings may be customized by partners via a customization package.
If apps override the defaults they must do so on every activity create.

Change-Id: Ib0af2411e82cdb95ffe3ff619150392c0a2bd883
7 files changed