feat(#472): Support discarding Changes

[SoulKa]

Changes

• Move save button out of URL input
• Use save icon for save button
• Add discard changes with eraser icon
• Fix discarding changes when there's no draft folder
• Fix race condition for editor content when switching requests

Testing

• Manual testing by switching requests and editing and restoring state
• Added automated tests for discarding

Checklist

• Issue has been linked to this PR
• Code has been reviewed by person creating the PR
• Automated tests have been written, if possible
• Manual testing has been performed
• Documentation has been updated, if necessary
• Changes have been reviewed by second person