PicSphere: First batch of enhancements [1/2]

This patch:
- Update prebuilt assets - these are going to disappear soon. See the
  second patch for details on the JNI part changes
- Add a libpopen_helper to let us run binaries through popen instead
  of Java runtime class (which used to freeze randomly for no reason)
- Make use of pto_gen/cpfind in place of autopano, which is much better
  and open up future enhancement possibilities (most noticeably, pre-
  alignment of images so that it doesn't spend multiple minutes trying
  to match each image separately, when we already know the relative
  position of each shot).
- Make use of multiblend instead of enblend, which works similarly but
  much faster (like, 172x faster)

PS2:
- Pre-align images using the gyroscope orientation to match only images
  that are next to each other.
- Reformat shell command calls to be cleaner (using String.format)
- Use constants for settings

PS3:
- Cancel the addition of linefind
- Remove autopano
- Raise PicSphere default quality
- Don't lock 2:1 canvas on PicSphere render
- Support multiple PicSphere being rendered at once
- Fix percentage progress with new steps
- Use multiblend --wideblend option
- Various stability and bugfixes

Change-Id: I6efea4ce6c1a3d97f63ab687a3779b9ca358e2d5