renderer: Sample the red component of depth textures

This makes sure to sample the red component of the shadow map depth
texture since, depending on what version of opengl is being used, and
what profile depth, textures can either behave like luminance (L,L,L,1)
textures or component red (R,0,0,1) textures. Since we were reading the
z component we would read 0 in some cases.
Make gstreamer an optional dependency
image-source: Add _get_natural_size() api
Use new cogl_gst_video_sink_get_natural_size() api
shell: strip out most android specific code
Guard xlib specific code
Add fmemopen fallback implementation for OSX and Android
Only check for avahi and gtk on Linux

This makes sure to only look for gtk (used for file open dialogs) and
avahi (used for ZeroConf device discovery) when building on Linux.
updates linux and osx build scripts and starts android build script

This updates the scripts for building linux and osx binaries of the Rig
editor.

This also adds an initial script for building a set of
PREBUILT_SHARED_LIBRARY modules for Android that can be used for
running Rig on an android device.

This also adds an android/project that contains an Android project that
can be used to build the rig-simulator.
fix: image-source: Add _get_natural_size() api
remove empty rig-simulator-service.c
Don't define RIG_EDITOR_ENABLED when building for Android
frontend: support listening on abstract socket for sim on Android
slave: remove android_main() since we now use SDL on Android
iterate how we track bindings

This iterates on the RigBinding code so that binding aren't only made as
a side effect of creating a RigBindingView. This enables us to
instantiate a RigBinding when unserializing a UI. This also hooks up
bindings to be activated and deactivated by a controller like other
properties.
binding: only build codegen code for editor
camera-view: use bool instead of CoglBool
fix: binding: only build codegen code for editor
camera-view: avoid referencing tools if not built with editor support
code: don't build codegen support when not supporting editor