Fix WebP usage.

* Introduce config variable USE_WEBP (ON by default, but disabled for unsupported archs WINRT and WP8)
* Set CC_USE_WEBP define according to USE_WEBP variable
* add WebP include directories to search patch only for libcocos compilation (it not used in public headers)
Unify usage of chipmunk library

* cmake/Modules/FindChipmunk.cmake now can find prebuilt chipmunk libs
* follow USE_CHIPMUNK variable (although at the moment cocos can't build without chipmunk)
* come cleanups and formatting