Build system

Build-system with the corresponding Android/iOS/OS X toolchains cmake files, mainly architecture changes with new CMake build files. 

**Architecture changes**
- CMake : The project now uses CMake, inside the **build/** folder there are the toolchain and utilities cmake files. The first called and used CMake file is in the root **/CMakeLists.txt** and then runs the different platform-dependent cmake files, which then run the CMakeFiles of the dependent libraries if needed (like Core/GLFW/JSon/GLM). Added two toolchains file, one for android grabbed from [here](https://github.com/taka-no-me/android-cmake/blob/master/android.toolchain.cmake), and one for iOS grabbed from [here](https://code.google.com/p/ios-cmake/source/browse/toolchain/iOS.cmake); these files define all the pre-required variables in order to use CMake for the corresponding platform.
- Core : is now used as a static library, and has its own CMakeLists.txt.
- Json : is now used as a static library as a dependency of the Core static library.
- GLFW : is now used a a git submodule.
- Changed somehow the architecture of the project : iOS/OS X platforms has now an **src/** folder where to put the sources, an **include/** folder for dependency headers and a **lib/** folder to put libraries if needed.
- Removed old Makefile
- Further improvements/work : 
    + Use CMake to build the UnitTests 
    + It could be a good idea to modify a bit the CMake toolchain for Core in order to be able to generate an executable for it; for test purposes. 
    + Check which files are still needed inside the **android/** folder considering the new toolchain for this platform
    + GLM : could also be used as a submodule from [here](https://github.com/g-truc/glm)
    + Curl : use the same headers/static fat library for both OS X and iOS


**Source code changes**
- Fixed some missing inclusions 
- Fixed some compiler/standard library issues to fit for g++/clang++ at the same time
- Curl : used headers from [this project](http://seiryu.home.comcast.net/~seiryu/libcurl-ios.html)
Last thing I'd suggest: I think GLFW should actually be an external dependency and not a submodule in the repository. 
 * We're already asking users to install a brew package for CMake, one more brew command is basically no effort. 
* The GLFW source is pretty huge and I'd prefer not to have it in the repo
* GLFW is pretty stable and we're not using any features that are at risk of breaking with an upgrade, so we don't need to hold it at a specific commit (if anything we'd probably benefit from updates to GLFW)