Improve browser extension options menu

Created by: AlicjaSuska

Part of RFC 221: Improve discoverability/awareness of the browser extension

Description

1. Layout changes
2. Add alerts

Design documentation

1. Layout changes See old vs. new layout comparison

• Header: a. update the logo b. remove the settings icon c. add more vertical spacing
• Info section: add headline and code hosts logos. When user is on the code host, highlight the proper icon.
• URL section: a. keep 'https://' permanently in the input field b. add error message c. when user clears the input - automatically fill out with sourcegraph.com d. add informative text e. add link to the Docs under 'How do we keep your code private'
• Advanced settings: moved to the bottom, under 'open advanced settings' button
• Add links to Sourcegraph Cloud and Docs at the bottom of the window

2. Alerts Add alerts to inform users about the current state of the extension, errors and actions they can take

• Grant permissions
• Private repository
• on sourcegraph.com
• on domains other than code hosts

Questions to answer Is it possible to identify when the user is on the private instance and add an alert: ‘We’ve noticed you’re on the private instance. Do you want to update your extension to point to the correct URL?’ - discussion in this comment @felixfbecker

Note from @AlicjaSuska : if it is impossible, let's move forward without the notification