feat: Command popup

[xavierchanth]

• Added a new field to MessagePopup called text_align for text alignment which defaults to Center.
  • Updated all references to pass None for message popup.
• Added a new popup called CommandPopup which is activated when : is pressed from any of the tabs.
  • The popup provides a TextArea which allows the user to run a jj command
    e.g. when help is typed, it will run jj help
  • Enter to confirm and execute the command
  • Esc to close the popup
• Commands with output or an error message will show it in a message popup using the left align
• Commands without output close the textarea and return to the view before running command popup (if they fail, they still show the error message)
• New action to refresh the current tab which is called after running a command

Open to design feedback, first time writing any Rust, so please bear with me if I've made some mistakes.

asciinema showing a brief demo of the PR: https://asciinema.org/a/wFns1WU24IicaUdgh1G3RmOgR