Swap themes & edit theme config from TUI

[bcorey]

CURRENT WORKFLOW
The theme switching UX looks like this:

1. blogr theme list
2. pick a theme name from a busy list
3. blogr theme set [name]
4. blogr theme info [name]
5. copy config fields into blogr.toml
6. set values

DESIRED WORKFLOW

1. blogr config edit
2. navigate to theme section
3. Instead of a text field, theme has enum options for each theme
4. selecting a new theme populates the theme section fields with the theme config options & adds them to the blogr.toml
5. Edit all the theme config options right there in the tui

ADVANTAGES

• no hunting for available config options
• rapid theme changes so new users can find one they like

benefits from #29 - we can split the theme list in the config TUI accordingly and only show blog themes or personal site themes depending on what the user is looking for.

[bcorey]

Work in progress:

theme-change-demo.mov