Themes: Use INSTALL_LOCATION_INTERNAL_ONLY for legacy icon packs

If an icon pack is currently applied and is installed using forward
locking, the system will crash when the pack is updated.  Several
applications can have the pack attached to their resources and this
causes the system to crash because it cannot unmount the asec container
to finish the post install process.  Installing these packs to internal
storage without forward locking alleviates this issue.

This is done with theme packs as well, including legacy themes.

Change-Id: I155fc0bd671f3f9baaf2565d1c4d654a0a5348dc
Themes: Use first asset entry for lockscreen wallpaper

The current implementation assumes the wallpaper will be named
either wallpaper.png or wallpaper.jpg.  If this is not the case
the wallpaper is not applied.  This patch implements the lockscreen
wallpaper the same way that the regular wallpaper is done.

Change-Id: I9f3dd299c1e61158fa53c163f7e42e21e2f9b1dc