Adds const to getters

Many getters in cocos2d are not declared as const.
This patch adds const to many cocos2d properties, specially in CCNode and
subclasses
Adds more const in getters

In Sprite and Texture2D
setTexParams() is passed as a const reference

All structs (PODs), should be passed as const reference.
eg: Size, Point, ccTexParams, etc... should be passed as const reference.
Merge branch 'const_love' of https://github.com/ricardoquesada/cocos2d-x into const_love
issue #2373:add const in pkg files
issue #2373:fix a compiling error
Merge pull request #3072 from minggo/const_love

Fix compiling errors of #3070