Provide presets (pre-built configurations with widgets)

Since the configurations are simply objects exported and read by the CLI, we could offer pre-built configurations with various options for the status bar (left), window management, theming, and more. ```typescript import { minimal } from 'better-tmux/presets'' export default minimal ``` Customizing: ```typescript import { minimal } from 'better-tmux/presets' export default { ...minimal, theme: 'nord' } ```