Fix keyboard shortcut if multiple windows are open

Fix: Make add-in work after idle unload

- Make background script work after idle phase
- Remove "settings" menue from toolbar button (functionality is always there), and add inserting both types of quotes
- Add Hungarian quotes and inverted Spanish question and exclamation marks.
- Fix some typos

Feature: Add inline quotes
API: Update to Manifest v3

- Update manifest.json from v2 to v3
- Update use of APIs accordingly
- Add inline quoting feature
- Remove obsolete firefox "undo" warning
- Change block quote keyboard shortcut on chrome from disfunct Ctrl+Shift+E to Alt+B
- Inline quoting receives its own keyboard shortcut: Alt+M
- The QuoteMe button in the toolbar can be configured to insert either inline or block quotes
- Using Shift+Click triggers the non-default action on the toolbar button (not available on chrome)
- Bump version to 2.0.0

Fix: Empty options should stay empty. In an attempt to provide default values if no options have been saved yet, any empty string provided as quotation mark was replaced by the default setting. Also add some sort of visual feedback after saving options.

Fix undo behavior in Firefox 89 and newer