Improve colour scheme

[nebbles]

Update the colour palette of the tool. Colour support, compatibility and 'fallbacks' need to be checked then doing this.

[nebbles]

Need to overhaul the colouring system. Need to move away from home-baked Ansi class. Probably best to move entirely to prompt toolkit, as it supports an easy to use styling system with custom colours etc.

[nebbles]

These are the colours I've been dealing with based on my configuration. They look decent in my terminal however in many others the colours are based on the configuration of that particular terminal. I've seen this - it can be hideous.

"""
iTerm configuration
===================

------- normal colours
#000000 black
#f04c24 red
#78c969 green
#f5d939 yellow
#19aaed blue
#a081d3 magenta
#19aaed cyan
#c6c6c6 white

------- bright colours
#000000 black
#e87162 red
#87c27c green
#f2db5c yellow
#4690dc blue
#a691ca magenta
#4aa9e9 cyan
#c6c6c6 white
"""