Sort print_info on ResolvedContext

Add an argument to allow the output of `print_info` method on a `ResolvedContext` to be alphabetically sorted.

We discussed making this configurable so that the global behaviour can be set for `rez env`, as well as adding a command line option.  I haven't had time to to this, and most likely wont before Christmas.  This keeps current behaviour and gets us part of the way there - I'll try and finish it off with a new pull request next year.