[Feature] Additional features worth adding before full release

[claration]

Request

• Clipboard bottom panel with options to switch to in settings
• HTML preview with app whitelist for bottom panel
• RTF preview for bottom panel
• Onboarding with default options, for example adding Keychain Access.app and Passwords.app before first full launch
• Finish preview when pressing spacebar

Request Agreement

• I have read the requirements for opening an issue above

Contributor Checks

• I am willing to add this feature myself