Allow specifying a theme when creating a Context

A Context normally loads the resources associated with the given
package that this context is for.  This patch allows us to specify
a theme we want attached to a given context's resources.

Change-Id: I1e619f038566233bd89ee96eb8eb87fa6894e630

Conflicts:
	core/java/android/app/ContextImpl.java
Use systemui's applied theme for notifications.

Notifications contain RemoteViews which are inflated using the
application's context for which this notification belongs to.  This
can look out of place if SystemUI is using a different theme than the
rest of the system.

This patch will use SystemUIs theme when inflating the RemoteViews,
giving us a more consistent look in the notification drawer.

Change-Id: I9514ce7fcc4858bad3d3c4190f55c1f5a1441d7c

Conflicts:
	packages/SystemUI/src/com/android/systemui/statusbar/BaseStatusBar.java
	packages/SystemUI/src/com/android/systemui/statusbar/StatusBarIconView.java
Themes: Add icon previews to ThemesContract

Change-Id: Icbfbee3404702a29881ad4933721d8beb39bef30
BaseStatusBar: Dismiss heads up on backpress.

Change-Id: I5b6191657cf0b74d825eb653a6e82c33e0527aad