rename loadAsset to loadColladaAsset

Signed-off-by: Wayne Wolf <wayne.ron.wu at gmail>
change log format and add some utility class

Signed-off-by: Wayne Wolf <wayne.ron.wu at gmail>
Load scene using assimp, commit 1

designed to contain assimp in a small number of files, scene element
definitions are mostly identical to assimp. This is a current solution,
in future, scene, mesh, animation format will be defined, assimp will
only be used offline.

Signed-off-by: Wayne Wolf <wayne.ron.wu at gmail>
Load scene using assimp, commit 2

Signed-off-by: Wayne Wolf <wayne.ron.wu at gmail>
optimize a load scene case

avoid calling vector push_back once and once again, and modify
mTriangleFaces fromvector of shared_ptr to vector of objects

Signed-off-by: Wayne Wolf <wayne.ron.wu at gmail>
remomve a log line

Signed-off-by: Wayne Wolf <wayne.ron.wu at gmail>
add a log line

show how many faces, need to optimize this in the future.

Signed-off-by: Wayne Wolf <wayne.ron.wu at gmail>
add a type cast function

Signed-off-by: Wayne Wolf <wayne.ron.wu at gmail>