Fix ResourceNotFoundException when updating  applied theme

If the user has a theme applied and there is an update to that theme,
then the themed apps will crash. This is because the theme's APK path changes,
but the apps do not update their resources. Apps were not updating their resources
because updateConfiguration() determined that the config (which only has pkgName) hasn't changed.

The problem is fixed by first applying the default theme config and then re-applying the
updated theme.

SystemUI was crashing with a NPE while verifying this fix, so a NP check was added to SystemUI as well.

Change-Id: I00e32fc1535b4d279fcb37c35f868501ecc1dd19
Themes: Support applying components from multiple themes [1/3]

The current implementation assumes the components being passed
into the ThemeService belong to the same theme.  This patch uses
a Map instead of a List to pass in a mapping of components to
package names, allowing us to apply several components from
different themes.

Requesting a theme change now takes a Map<String, String> which
maps components to the theme package name they will be applied
from.
Example:
    Map<String, String> componentMap = new HashMap<String,String>();
    componentMap.add(ThemesColumns.MODIFIES_ICONS, "com.mytheme.blue");
    componentMap.add(ThemesColumns.MODIFIES_OVERLAYS, "com.mytheme.red");

    ThemeManager tm = (ThemeManager) contex.getSystemService(Context.THEME_SERVICE);
    tm.requestThemeChange(componentMap);

Change-Id: I13fa17eabecb824884fe522d5dc1822a4d7c55f4