Code Listener's settings can be now controled from user's environment.

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.

Supported values  (case-insensitive): ```ON/OFF, TRUE/FALSE, 0/1/2/3/4```

**Example:**
```bash
export CL_DEBUG_GCC_TREE='true'
```

This is mostly useful for developers -- my suggestion is adding the same functionality for other parts of the predator also.

The ```CL_DEBUG``` was also introduced -- e.g. ```export CL_DEBUG='ON'``` can be used -- to compile the CL with the ```NDEBUG``` turned OFF.

**Environment default settings:**
If the user doesn't have any exported CL settings values, the updated [switch-host-gcc.sh](https://github.com/deekej/predator/blob/upstream/CL-env-settings/switch-host-gcc.sh), [switch-host-clang.sh](https://github.com/deekej/predator/blob/upstream/CL-env-settings/switch-host-clang.sh) and [run-llvm-tests.sh](https://github.com/deekej/predator/blob/upstream/CL-env-settings/run-llvm-tests.sh) scripts behave same as before. Setting the environment and switching it back also results in the default behaviour (before the update).

**Consequences:**
Because of it, the ```cl/config_cl.h``` has been moved as ```cl/config_cl.h.default```. The ```cl/config_cl.h``` still has the same functionality and is used for inclusion in other files when compiling CL, but it is being modified depending on the users settings. It is therefore not tracked by git anymore, it is always copied from default file and updated depending on user's environment settings.

Initial build through

**Other changes:**
The colored output for ```ClPrettyPrint()``` can be now configured from Code Listener's config also and it has been turned OFF by default.

**Supported environment settings:**
  - CL_DEBUG_COLORED_OUTPUT
  - CL_DEBUG_CLF
  - CL_DEBUG_GCC_GIMPLE
  - CL_DEBUG_GCC_TREE
  - CL_DEBUG_LOCATION
  - CL_DEBUG_LOOP_SCAN
  - CL_DEBUG_POINTS_TO
  - CL_DEBUG_VAR_KILLER
  - CL_EASY_TIMER
  - CL_MSG_SQUEEZE_REPEATS
  - CLPLUG_SILENT
  - DEBUG_CL_FACTORY

Best regards,

Dee'Kej