Make theming editable - Githubissues

The theming of the app should be editable.

TODO

[x] add example theme file
- [x] also add files for each theme, so that they could be modified
[x] add cli option to load theme from json file
[x] add cli option to load build in theme (default_old and dracula)
[x] make theme get auto loaded if a theme file exists in config directory
- [x] Is dependent on platform, under linux it will be in ~/.config/alpha_tui/theme.json, in windows it will be {FOLDERID_Profile}/.config/alpha_tui/theme.json
- [x] theme provided via cli option overwrites default theme in this config directory
[x] fully implement dracula theme (mean there will be more fields to be editable)
[x] update documentation
- [x] how to write custom theme (show example theme file)
- [x] that theme can be placed in .config/alpha_tui/theme.json and that theme is loaded automatically from there