Update Utils.js

If there is an empty ImageTexture node (its url is empty) in x3d world, doc.downloadCount never decreases to zero in Firefox (image.onload() and/or image.onerror() does not get called). This means that progressDiv is still visible. Fix for this is obvious -- doc.downloadCount is not increased in x3dom.Utils.createTexture2D() if url is empty and texture is immediately returned instead. Solution tested in x3dom 1.5.1 only.
removed special code for preventing 'texture not complete' warning as this breaks rendering on certain platforms (at least some OSX)
Merge pull request #224 from stepasite/patch-1

Update Utils.js
initial check-in of AR with WebRTC
fixed Viewfrustum (matrices were transposed) and projection matrix of AR demo
cleanup of AR test
added AR example
local texture
Internal centerOfRotation for Viewfrustum and reactivated 1-pixel intermediate textures
added multi-marker example
removed 1-px intermediate CubeTexture since this leads to computer crash on certain mac systems
4 pixels instead of 1
used variable for transcoder state
parent type check
mirror example
updated index.html
comment
Update runtime docu
Regenerate changelog
Releasenotes