adds support for addon_config.mk

source, libs, include search paths and their exclusions should work as it is for every platform

also the Addon class now has:

   - dependencies: other addons with which this one depends
   - cflags: compiler flags that need to be added to the project
   - ldflags: linker flags that need to be added to the project
   - pkgConfigLibs: only linux, already parsed by the makefiles no need to modify anything in the PG
   - frameworks: only osx, frameworks required by the addon, need to be added to the project
   - data: data file that should be copied to the example data folder
   - metadata: no need to use it by now

this ones are correctly parsed in the Addon class but need to be added to the specific projects when adding addons to them