Improve the browser extension

[Jenselme]

To improve the raw result made in #156

• Publish the extension.
• Ask confirmation before reseting options to default.
• Provide better error messages if the extension is used with its default configuration.
• Can delete an article after confirmation directly from the extension.
• Can unsubscribe from a feed after confirmation directly from the extension.
• Don’t override title or reading time if manually set when resaving article. It’s a bigger problem here because if we reopen the extension, the values we set will be erased.
• Don’t override read status in this case: the extension will display it, no need to force it like we do when adding in the form.
• Support sub tags too!
• Can save article and subscribe to feeds without closing the extension.
• Setup for translation.
• Can test the options directly on the options page.
• Improve display with a huge number of tags.
• Can go to the saved article directly from the extension.
• Auto save form updates (and display a saved status)? It’s not that great to have to update after editing tags.
• Display whether we are subscribed to a feed when opening the extension.
• Display whether we already saved the article when opening the extension.
• Display message stating it must be configured if it’s not.
• Provide a way to test the connection to the API directly from the configuration page.