Added virtual to UIWindow destructor

Fixes issue #198. See http://stackoverflow.com/questions/461203/when-to-use-virtual-destructors
Fixed screen root entity being adjusted by default, fixed image alpha premultiplication
Merge branch 'master' of https://github.com/ivansafrin/Polycode
Merge pull request #206 from CIB/cleanup

Added virtual to UIWindow destructor
Added a flag to renderer to treat normal blending as premultiplied, made the screen entity size default to 0 instead of 1
Merge branch 'master' of https://github.com/ivansafrin/Polycode
Fixed collision only entity not setting rotation correctly
Fixed point collision examples
Merge remote-tracking branch 'upstream/master'
Basic 3D editor file loading and 3D Entity template