Create browser-action UI

Let's add a button with app's logo (which need to be created). On click, it
should show a popup with following contents.

1.  UI to configure whether new tabs opened in browser should be auto-chained
2.  If new-tab-auto-chaining is enabled, UI to configure which (if any) groups
    should be auto-assigned to new tabs e.g a list of of groups with a chain icon
    in the end

