Adds an option to copy the RSS link to the user's clipboard when the button is clicked, instead of opening the link in a new tab.

The current behavior (open in a new tab) is kept by default and can be changed in the extension's options page.

Fixes RSS feed URLs for some comics (see https://forums.tapas.io/t/rss-feeds-gone/41724/6)

- Add support for mobile site m.tapas.io
- Open rss feed in a new tab

Webextension icon added