Changed link to placeholder images for Wooclap Slides

Fixes on question insertion and question play on the slideshow following the latest Google Slides update.

Fix Question Insert button keep running

Removed action to write in speaker's notes

Fixed an issue with a changed class selector breaking the insertion of slides.

- Fixed an issue where it was not possible to insert a Wooclap question into Google Slides.

- Fixed an issue where keyboard shortcuts did not work properly.

v1.0.6

- Fixed an issue where the extension didn't work in Firefox.
- Greatly simplified the code: there's no longer a CSS file, nor a background.js file.

v1.0.5

- Removed unused storage permission.

v1.0.4

- Updated the placeholder images to use the new branding.
- Updated the store images to use the new branding.
- Fixed an issue where the Wooclap vote would not start when quickly switching to a Wooclap vote after starting the presentation.
- Fixed an issue where the Wooclap vote was not displayed if the user was not logged in.
- Fixed an issue where the Wooclap vote was not displayed if the user was logged in on the wrong account.

- Fixed a bug where the Wooclap question would not start if the Google Slides presentation had transition enabled.

- Update placeholder image text in French.