Add theme support

[boolean-maybe]

Summary

tiki must support customizing via themes

Background

Is your feature request related to a problem? Please describe:
currently color scheme is hard coded. User must be able to provide custom themes

Describe the solution you'd like:
At a minimum support light/dark theme. Ideally themes should be specified via YAML config files

Describe alternatives you've considered:
A minimum solution would detect user terminal settings and set light/dark theme automatically

Details

A theme should only specify a palette - a set of colors that play well together. A theming solution would apply a single color across multiple components

Outcome

Support for light terminal and customizable look