Export Tabs URLs (Containers) tekijä re-inverter

This is a clone of https://addons.mozilla.org/en-US/firefox/addon/export-tabs-urls-and-titles/ with support for firefox containers.

I recommend the following configuration for firefox container support.

enable container tracking from settings then place the following in custom format and then tick custom format from drop down.
- [[{container-url}{url}][{container-title}{title}]]\r\n

# Features

- **Include titles** : ETU provides a default format which displays titles along tabs URLs ;
- **Custom format** : optionally, custom patterns can be defined instead of the default "include titles" one (e.g. markdown) ;
- **Filter tabs** : ETU provides a RegExp-enabled tabs filter ;
- **Limit to current window** : optionally, the list can be limited to the current window ;
- **List non-HTTP(s) URLs** : optionally, ETU can list each and every tab, including cases where the URL scheme isn't HTTP(s) ;
- **Track containers** : optionally, prepend information about the container of every tab in [Open external links in a container](https://addons.mozilla.org/en-US/firefox/addon/open-url-in-container/) extension format

## Permissions

- **Access browser tabs** : required to list the tabs ;
- **Input data to the clipboard** : required to copy the list to the clipboard ;
- **Display notifications** : not required stricto sensu (as the extension could work without it) but it is used to improve the user experience by providing visual feedback about what is going on ;
- **Storage** : required to store settings.