As a user I want to share multiple tabs

[mindrones]

[depends on: #172]

Say we have 4 tabs we're working on and we need to share 2 of them with someone by pasting the URL of those 2 tabs in an email or in a social network.

In the tabs panel, we need to be able to:

• select multiple tabs (using the tabs checkboxes)
• hovering the "share" icon in the panel controls we show the message "Copy a shareable link to your clipboard" in the status bar
• create and copy the URL with the 2 selected tabs in the clipboard
• show a tooltip in the status bar with a message "Link copied to your clipboard"
• make the tooltip fade away after 3 seconds
• deselect the selected tabs