Fix addy.io branding (Addy.io -> addy.io).
Add an icon for the extension and its compose action button.

Implement a workaround for the problem that sometimes the popup window was too small and therefore not showing all of its content.

Fix a bug which prevented the domain options from being reloaded from Addy if the user changed their API key or host URL (an unlikely scenario, but still, since we found the bug we should fix it).

Add a link to the Addy.io web app to the bottom of the compose window pop-up.

Bug fix: When the message has recipients but none of them are eligible for being replaced with Addy addresses, the pop-up wasn't displaying that properly.