Themes: Pass resource IDs instead of bitmaps [1/2]

Rather than passing around bitmaps in the ComposedIconInfo we
can pass the resource IDs associated with each of the components
and retrieve those drawables when composing the icon.

Change-Id: If855e60e505571f25316e6728e423fbee62c32d3
Themes: setUserRequired(false) when updating audibles

This prevents the following exception
F/Environment(18007): Path requests must specify a user by using UserEnvironment
F/Environment(18007): java.lang.Throwable
F/Environment(18007):   at android.os.Environment.throwIfUserRequired(Environment.java:787)

Change-Id: Ic6ac7537079ed27912c40683c877e05992b708e9
Themes: Build icon cache when applying icons

The theme service will schedule building of the icon cache when
an icon pack is applied.  This will allow the icon cache to be
populated immediately after icons are applied rather than build
it up as icons are requested.

Change-Id: I453eda5f6298ff79e22827c622a0eddcab9c721d
Themes: Allow clearing the wallpaper and ls wallpaper

By providing an empty string for the MODS_LAUNCHER and
MODS_LOCKSCREEN components, the theme service will clear out any
existing wallpaper the user had set.  This provides the same
functionality as if the user was picking "No wallpaper" from the
picker.

Change-Id: I0c349ad4afa2bcef2c302105315709786510c0aa