Setting the Code Listener from shell environment automatically.

Users can now put the ```export CODE_LISTENER_OPTION=VALUE``` in their .bashrc file to permamently change the values of Code Listener they require, without affecting the git's tracking system.
Example:
------------
```bash
export CL_DEBUG_GCC_TREE='true'
```
Supported values are (case-insensitive): ```ON/OFF, TRUE/FALSE, 0/1/2/3/4```
This is mostly useful for developers -- my suggestion is adding same the functionality for other parts of the predator also.

EDIT: The ```CL_DEBUG``` was also introduced -- e.g. ```export CL_DEBUG='ON'``` can be used -- to compile the CL with the ```NDEBUG``` turned OFF.

If the user doesn't have any exported CL settings values, the updated *switch-host-gcc* script behaves same as before. Setting the environment and switching it back also results in the same behaviour as before.

Because of it, the ```cl/config_cl.h``` has moved as ```cl/config_cl.h.default```. The ```cl/config_cl.h``` still has the same functionality, but is being modified depending on the users settings and is therefore not tracked anymore by git.

Also, the colored output for ```ClPrettyPrint()``` can be now configured from Code Listener's config and it has been turned OFF by default.

Lastly, I want to merge the last commit only, but for some reasons I can't create such a pull request. Github shows me the previously merged commits as if they were not. I hope this will not be an issue.

Best regards,

Dee'Kej