Split source tree into separate libraries

Split source tree into separate libraries

Now the repository contains several packages. Each package is a separate
library or a bin program. Followings are brief descriptions of directories.

===============================================================================
pepper	      |  Pepper core library package.
-------------------------------------------------------------------------------
render        |  Rendering library (pixman, OpenGL)
-------------------------------------------------------------------------------
desktop-shell |  Desktop shell library
-------------------------------------------------------------------------------
drm           |  DRM output backend library
-------------------------------------------------------------------------------
libinput      |  Libinput input backend library
-------------------------------------------------------------------------------
wayland       |  Wayland output/input backend library
-------------------------------------------------------------------------------
x11           |  X11 output/input backend library
-------------------------------------------------------------------------------
utils         |  Utility library
-------------------------------------------------------------------------------
samples       |  Sample programs for testing pepper libraries
-------------------------------------------------------------------------------
doctor        |  Reference server using pepper libraries
===============================================================================

Renderer is no longer a core object, instead, output libraries can freely use
it by linking against separate libpepper-render.

pepper_output_schedule_repaint() is now exposed as an API.

Put utility functions on the pepper-utils package.

Need a build script which takes options for enabling or disabling each library.

Change-Id: I5c686d158ea61056cd517f29c4eda4b2d4c7877a