Resolved Context Info Colour

Update the `print_info` method on a resolved context to include colour highlighting in the output (I'm not able to attach a screenshot showing the change - GitHub shows an error when uploading).

This makes it easier to visually identify local, implicit and not found packages, as well as different sections of the output.  

The colour escape sequences are provided by an external package called colorama (https://pypi.python.org/pypi/colorama), which I have added to `rez.vendor`.  This should be cross platform (I have tested on OSX and Linux).  The output looks ok on a black or white background, so should be ok with most terminal themes.

I have also added a specific section to show local packages.  This has been requested numerous times by developers here to make debugging and replicating environments easier.

The formatter has been made configurable so that installations can switch back to the default 'simple' formatter if required, or extend the implementation further.  It is also possible to pass a `formatter` instance to the method so different sections of Rez's execution can retain control if they require.

I am not overly happy with the implementation of this feature, but it does make the output for `rez env` nicer.  I am open to suggestions for improving the implementation.

This branch was taken from the 2.0 at the beginning of the week as it wasn't clear what the state of the other branches was.  I don't think it will introduce conflicts, but might require modifications with respect to the change from `settings` to `config`.