Change the rest of the attributes interfaces to pass parameters by const ref instead of per value.

git-svn-id: svn://svn.code.sf.net/p/irrlicht/code/trunk@4726 dfc29bdd-3216-0410-991c-e03cc46cb475
- Collada dae-loader now set's the vertex colors (thx @sf17k for report and test-models)

git-svn-id: svn://svn.code.sf.net/p/irrlicht/code/trunk@4727 dfc29bdd-3216-0410-991c-e03cc46cb475