create install.py to set environment variables needed by cocos2d-x

* Set environment variables: `ndk_root` and `cocos_console_root`.
* Because there is not API in python to set system environment variables, so i add it in `~/.bash_profile` on linux and Mac OS X, and modify register table on Windows.  Any other elegant way?
* After setting environment variables, any way to make it take effect immediately? I want to use the environment value to use `cocos-console` after `install.py` return, like this
```shell
./install
cocos project new ...
```
I wanted to use `os.system()` to do it, but found it would create a new process.